To be even more specific:
Pentium 4 1.6Ghz 400fsb socket 478 (No HT) https://theretroweb.com/cpus/1512
Intel D845BG Mainboard https://theretroweb.com/motherboards/s/intel-d845bg-billings

Try driver 93.71. Using 307.83 with a Geforce 6600 is a very bad idea..

I tried using 175.XX (can't remember exactly not at my system) and it still had the same issues. DVI just works until after BOOT and Windows loads.

I got a little confused reading that, I'm not entirely sure your GPU is in one piece. Is your VGA output always having that purple-ish hue you described, even in the BIOS or from a DOS Prompt?

If we assume that hardware issues are not an issue, it seems to me you may have borked something when attempting to uninstall the older drivers. As user Tom.. said, 307.83 are from 2013, many years after the GF6 series had left any sort of relevancy. I'd recommend using something more period correct like 77.77 from 2005 or 93.71 from 2006 as Tom.. suggested. The vanilla 6600 was never a phenomenal performer so don't expect it to go much farther than 2004-2005 when it comes to games, certainly not with a Willamette 1.6GHz, a CPU that is often trading punches with a PIII 1GHz and very outdated by 2004 when this GPU was released.

My recommendations are as follows:

a) Take good, clean pictures of the videocard, both front and back, and post them here so we can help you detect if there's something wrong or missing on the PCB, ideally comparing it to high-res photos from online.

b) Nuke that WinXP installation or perhaps try a new one on a different HDD so we can take the software side out of the equation. Install WinXP SP1 or SP2 ideally (avoid SP3 as it is significantly more bloated and your P4 will struggle), then proceed with the installation of i845 chipset drivers from Intel, followed by your audio card drivers (are you using an add-on soundcard or the onboard audio?) , then your GPU driver, then DirectX 9c and lastly network card/on-board network if you have. If DVI is still giving you trouble, use VGA to boot and then see if there's some option in the control panel related to DVI activation.

Unrelated, but how much RAM do you have installed on this system?

Yeah, I had similar issue. You totally can bork DVI output on pre-8xxx series cards with late drivers. No amount of driver reinstall would help - card won't just be recognized as primary output device, unless you have a second card (newer or from different brand) to reassign it manually. There's something in the left-over registry which creates conflict with an output.

Garrett W wrote on 2023-04-18, 16:54:

I got a little confused reading that, I'm not entirely sure your GPU is in one piece. Is your VGA output always having that purple-ish hue you described, even in the BIOS or from a DOS Prompt?

Apologies for the confusion, the card in VGA has the purple hue even when in BIOS. I can color correct the monitor but not perfectly, I have tried older drivers now for the DVI output to little success but maybe even the 175.xx driver is too new although I don't believe that is the case. I can try even earlier later tonight.

My original questions are easier understood split up into two.

VGA is definitely a hardware issue, whereas DVI could be a driver issue.

As to your last question, I'm running 2x1GB 266mhz sticks of ram. Max supported speed on this motherboard being 266.

My pentium seems to actually enjoy SP3 although if you think it'll make a difference I can try loading SP2 on a different drive so I don't have to wipe all my files in this one.

The Serpent Rider wrote on 2023-04-18, 17:24:

Yeah, I had similar issue. You totally can bork DVI output on pre-8xxx series cards with late drivers. No amount of driver reinstall would help - card won't just be recognized as primary output device, unless you have a second card (newer or from different brand) to reassign it manually. There's something in the left-over registry which creates conflict with an output.

Does DDU not do enough to remove these issues from the registry? I found a version that seemingly works well in XP and killed off the fx5200 drivers as well that it found.

No idea. But more old-fashioned uninstallers had no positive result. Perhaps newer drivers create some soft of "shadow card", which is always assigned as a primary device by OS.

What are the chances you know which registries to edit haha.

I might go snooping around and see if I can find any hints of them.

Different driver versions appear to not be working properly, might need to get a new install of windows like recommended.

Ok guys, I spent way too long trying a bunch of different things that didn't work. Got the idea to try plugging in both the VGA and DVI cables at the same time...

Windows XP booted properly (purple screen all throughout boot so I knew it was VGA) and I then went into the NVIDIA control panel. Under monitor configuration I noticed I could now choose which monitor I wanted to display, so I changed it to 2 of 2, I assumed being the DVI connection andddd it worked!

Don't have to deal with purple anymore and I really hope this can help somebody in the near to late future with the same issue. Fixing the purple will probably be something I have to do at a later time but now I don't have to sacrifice color quality!

Hi Charleston,

You are having a hardware problem with your graphics card, one channel is dead, seems this problem might be frequent, as I had the same problem with my 6800 and 7800 AGP cards.

I overcome this problem similar way as you did - I used a DVI to AGP adapter and the problem went away (well, it's still here, just I don't care anymore 😁)