Gotta love that clunky AMD AGP north bridge.

Just a check as you don't mention it explicitly: you do have the AMD 761 chipset AGP drivers installed don't you? If not, that could explain a bit.

The WinXP AGP miniport driver isn't easy to find, AMD no longer has it on its site. This looks like the right one, but don't have a 761 board, so can't check I'm afraid, did scan it and seems clean at least:
http://www.opendrivers.com/download/driver-16935.html

dionb wrote on 2021-10-17, 23:30:

Just a check as you don't mention it explicitly: you do have the AMD 761 chipset AGP drivers installed don't you? If not, that could explain a bit.

The WinXP AGP miniport driver isn't easy to find, AMD no longer has it on its site. This looks like the right one, but don't have a 761 board, so can't check I'm afraid, did scan it and seems clean at least:
http://www.opendrivers.com/download/driver-16935.html

Thank you very much for your answer @dionb. The OS is a Windows Media Center 2005 and all the best working drivers are installed properly, as is the miniport driver. As there is a hardware change, Windows starts using its default VESA driver, the very same it uses when in starts in Safe Mode or during the installation process. With the glitches, it would be very difficult to install it and of course to install any driver. You can see the photos.

I just think that l should try to uninstall the AGP driver to see what is happening. Maybe there is a bug with it preventing some newer AGP cards to work well. But as I tried to start Windows in Safe Mode with the driver normally disabled, that was the same. That should have been to easy 😉

I'm open to any other idea.

Datadrainer wrote on 2021-10-18, 08:48:

[...]

I'm open to any other idea.

Before doing anything drastic, I'd want to be sure if it's hardware or software.

Try booting from a Linux LiveCD/USB (if the board can boot from USB) like an older version of Knoppix (4.x or 5.x should work fine on this hw). If you see the same glitching there, it's hardware and nothing Windows settings or drivers can solve. If it looks good there it's software and worth messing around with drivers etc.

Hi again,
I forgot to mention that the problem is the same whether I am using a VGA or DVI cable or whatever screen, CRT or LCD.
I burned a KNOPPIX 5 Live CD. The test runs without problem. The graphical boot menu displays normally. Then during the detection phase, the configuration tool detected the 7600 GS and configured Xorg to use the open source non-accelerated nv driver. Then the desktop shows, working perfectly (with no glitches at any resolution and refresh rate and all of that smoothly). Here are some screens:

Then, because I remember that post XP Microsoft OS loaded a graphical installation GUI from the beginning (meaning without copying files to the HDD before that), I decided to try an installation DVD of Vista x86-32, and I got that:

If I wanted to be a scandalmonger and start the controversy I would say here we have here a proof of the superiority of GNU/Linux over Windows 🤣. But to be serious, that only means Windows manages things differently from Linux (at least the 2.6 version), maybe by bypassing some BIOS information that Windows is using. So maybe there is something to do here. I tried to change some setting to Auto values but that haven't changed anything. The BIOS have extensive options for AGP configuration and I haven't the knowledge to know what advanced parameters I have to change... So, for that, I switch between the default BIOS settings to Auto. I have set the Signal Driving option to Manual only to show the options in case something can be done here:

Edit: I also tried to switch from UC to USWC.

Proper installation succeeds with this sequence:

Install Redmond OS using PCI graphics card installed
Install chipset AGP GART miniport and AGP drivers
Remove PCI card, insert AGP
When Redmond OS starts, it will activate the correct drivers that you installed in the previous steps

I have that same motherboard but have only used ATI cards in it and I have never had a problem, never tried a NVidia card in it.

If you need it I do have the original driver disk that came with the MB when I bought it.

retardware wrote on 2021-10-18, 16:44:

Proper installation succeeds with this sequence: […]
Show full quote

Proper installation succeeds with this sequence:

Install Redmond OS using PCI graphics card installed
Install chipset AGP GART miniport and AGP drivers
Remove PCI card, insert AGP
When Redmond OS starts, it will activate the correct drivers that you installed in the previous steps

Thanks @retardware, I have figured this myself, but not tested it because it is not very practical. Even if the driver works, having to swap video cards each time I want to install an OS or start in Safe Mode because something went wrong is not for me a solution. What I was looking for, is more a way to solve the glitches problem if it is possible. But following your advice, I decided at least to know if, when its drivers is installed, the card can operate properly. And it did .... well for a time. installed the last driver to support the card, the 307.83 version and it works as it should (nice picture without glitches). But after a random time, sometime at the login screen, the screen goes blank and the computer freeze. So unfortunately that does not solve anything 🙁 But maybe its a problem with the driver itself or a service/software associated with it.
In a first time I would like to find what is causing the glitches. KNOPPIX worked because of using the nv driver, but the more I think about it, and the more it seems to be a problem is related to VESA BIOS Extensions with the BIOS having difficulties to manages the mode of latter Nvidia AGP cards. But it can be a problem with the AMD 760 handling VESA video modes too...

Grem Five wrote on 2021-10-18, 23:56:

I have that same motherboard but have only used ATI cards in it and I have never had a problem, never tried a NVidia card in it […]
Show full quote

I have that same motherboard but have only used ATI cards in it and I have never had a problem, never tried a NVidia card in it.

If you need it I do have the original driver disk that came with the MB when I bought it.

Thank you for your answer and your offer, that's nice of you. But I'm lucky to have kept the box and all of its original content including the driver disc during all this years.
Your experience confirm what I have tested. All AGP ATI cards I tested are working great, Nvidia card only work to GeForce 4 series.

If there is no clean solution, maybe I'll continue to use a GeForce 4 on it for now, and buy a powerful AGP ATI card later.
I still can remake another K7 I was using long ago. It was more powerful, being built around an A7N8X-E Deluxe and a GeForce 7800 GTX. Their boxes are covered by dust so maybe it's time to use them again. What I wanted originally is to have access to the SSE instruction set on a machine from the 2000-2002 era but with a powerful video card from 2004-2005. And as I loved the A7M266 back in the day, I thought it was perfect for that.

@Grem Five, can you please tell me the fastest ATI card you tried on your A7M266? Thank you. I'm not very fond of ATI from this era because of terrible drivers. In games it was a nightmare with missing textures, display glitches, bad framerate... From the Rage 128 to the R100, things goes a little better though. And from the R200 to R500 a huge step was done on that. So a latter one, maybe a R520 could fit the PC well. If confirmed working, what about an ATI Radeon X1800?

Edit: I remembered wrong because apparently, the x1800 seems to exists only in PCI-E, so maybe a X850 Pro or X1650 Pro?

If you haven't already, is it worth experimenting with the various BIOS settings? I think I remember having a video card that wouldn't work reliably with Fast Write enabled. I'd try turning off 4x and Fast Write, putting Compensation and Drive Strength to Auto and disable AGP to DRAM Prefetch. I don't actually know exactly what they do, but generally disabling features makes it more likely that cards will work, if a bit slower. The BIOS might also have some sort of 'Load Fail Safe Defaults' option that should select some pretty conservative options. It could be that the linux video/chipset drivers are just less aggressive/buggy than the Windows ones.

snufkin wrote on 2021-10-19, 09:49:

If you haven't already, is it worth experimenting with the various BIOS settings? I think I remember having a video card that wouldn't work reliably with Fast Write enabled. I'd try turning off 4x and Fast Write, putting Compensation and Drive Strength to Auto and disable AGP to DRAM Prefetch. I don't actually know exactly what they do, but generally disabling features makes it more likely that cards will work, if a bit slower. The BIOS might also have some sort of 'Load Fail Safe Defaults' option that should select some pretty conservative options. It could be that the linux video/chipset drivers are just less aggressive/buggy than the Windows ones.

Thank you @snufkin. Maybe it can work indeed. Except for the Fail Safe BIOS option, I thunk of modifying this options, but I decided to not touch them because the idea of using a powerful video card was to use it at its maximum capacity otherwise I have no reason to change my GeForce 4.
But there is a lot of other options that I do not understand precisely what they do and how to configure them as the Compensation, Signal Driving or Delayed Transaction. Maybe there is something to do here without losing any perf but I don't know what.
So as I say, I will try an ATI card afterward. On this point I am counting on the community to orient me on a card adapted to what I am looking for. And I keep the GeForce 4 for now. Quite limited for some games, but work great for most.
But just to see what the BIOS will default, I'll try the Fail Safe option, I remember there is one and will let you know.

Datadrainer wrote on 2021-10-19, 09:12:

@Grem Five, can you please tell me the fastest ATI card you tried on your A7M266? Thank you. I'm not very fond of ATI from this era because of terrible drivers. In games it was a nightmare with missing textures, display glitches, bad framerate... From the Rage 128 to the R100, things goes a little better though. And from the R200 to R500 a huge step was done on that. So a latter one, maybe a R520 could fit the PC well. If confirmed working, what about an ATI Radeon X1800?

Edit: I remembered wrong because apparently, the x1800 seems to exists only in PCI-E, so maybe a X850 Pro or X1650 Pro?

The card I have in it now is a 9800 XT, way overpowered for the 1.2GHz Thunderbird I have in it. I have been trying to find a reasonable priced AGP X850 of some config but been unable to.

I have a X800 XL I have used in another machine thats PCI-E I liked but so far the X8xx AGP ones have been eluding me. =/

Grem Five wrote on 2021-10-19, 20:25:

Datadrainer wrote on 2021-10-19, 09:12:

@Grem Five, can you please tell me the fastest ATI card you tried on your A7M266? Thank you. I'm not very fond of ATI from this era because of terrible drivers. In games it was a nightmare with missing textures, display glitches, bad framerate... From the Rage 128 to the R100, things goes a little better though. And from the R200 to R500 a huge step was done on that. So a latter one, maybe a R520 could fit the PC well. If confirmed working, what about an ATI Radeon X1800?

Edit: I remembered wrong because apparently, the x1800 seems to exists only in PCI-E, so maybe a X850 Pro or X1650 Pro?

The card I have in it now is a 9800 XT, way overpowered for the 1.2GHz Thunderbird I have in it. I have been trying to find a reasonable priced AGP X850 of some config but been unable to.

I have a X800 XL I have used in another machine thats PCI-E I liked but so far the X8xx AGP ones have been eluding me. =/

Thanks for the answer. Then I'll wait for a affordable X850 one to appear in my area. The only cons is the R400 is only compatible with DirectX 9.0b. But that's not so important as most DirectX 9.0c games I have require a more powerful CPU and GPU to work with fluidity anyway.