You could try to clear the rtc ram of the cmos. The exact procedure is described on page 1-21 of the manual. And use a new battery just in case.

Thanks, y'all! I'll try these things tomorrow (starting with the yellow/black 4-pin thing). Too exhausted to try again tonight, but I'll let you know what happens!

Was about to suggest a dead coin cell battery as a possible cause, but more worryingly I just noticed that in the 3rd pic of your original post you appear to have the 4 pin section of the atx 20+4 main power connector plugged into 12V cpu connector (and yes I just tried and it does fit!) so you're got +3.3V & ground on the 12V pins and +5V & +12V1 on the ground pins - not a good idea!!!.

K this may sound crazy. To rule out the slim chance you have a bad power button.

Find a little flat head screw driver, like the mini kind. And short these pins. Touch the screw driver to the 2 pins at the same time and see if it come on.

That means short the power switch header indicated by the 2 red lines, like a button would do but with a screw driver instead.

PC Hoarder Patrol wrote on 2020-08-26, 04:14:

Was about to suggest a dead coin cell battery as a possible cause, but more worryingly I just noticed that in the 3rd pic of your original post you appear to have the 4 pin section of the atx 20+4 main power connector plugged into 12V cpu connector (and yes I just tried and it does fit!) so you're got +3.3V & ground on the 12V pins and +5V & +12V1 on the ground pins - not a good idea!!!.

Yeah, a couple other people pointed that out earlier. This is only the second computer I've built, and unlike the first one (which I built like 5 years ago, so I don't remember a lot of the specifics), this power supply didn't come with any documentation, so I just kinda did my best. I assumed that, since the power connectors are keyed, I wouldn't be able to plug in the wrong connector. What's the point in keying them if that still lets you get it wrong?!

Anyway, I've found the correct connector now - thanks to the previous commenters pointing out that what I had thought was a single 8-pin connector was actually two 4-pin connectors hooked together - so I'm going to try again in a bit. Hopefully it works this time.

Partial success! I've managed to get it to POST.

The POST screen flashes for a second and then goes blank. The speaker gives me one long beep and then four short beeps. According to https://www.asus.com/support/faq/1029959/, that means:

An anomaly is detected on CPU Fan Error or CPU Over Temperature Error or CPU Over Voltage Error

Please ensure your CPU and CPU Fan is installed correctly, if still fail, please enter BIOS to load default BIOS or clear CMOS to try again

I've cleared the CMOS (I assume that does the same thing as entering the BIOS to load default BIOS? But lmk if I'm wrong.) and the same thing happens. As far as I can tell, the CPU and CPU fan are installed correctly, and the fan does spin up now.

I do have another CPU and cooler that I can try. Would it be a good idea to swap them out at this point, or is there anything else I should try first?

Also, is this confirmation that the motherboard itself is working, or is there still a possibility that there's a problem with it?

Sounds like the HSF might not be mounted correctly. You might want to take a look at the bottom of the motherboard and make sure that all four pins of the HSF are inserted and locked correctly. They each has a semi white colour sleeve that is split into two halfs and a black pin at the centre. Be careful when inserting the semi white sleeves as they could bend and break easily.

The way to properly release them is to turn the back knobs counter clockwise, then pull up all the way. Good practice is to release 2 diagonal posts first, follow by the other 2 diagonal posts.

To reassemble, first remember to apply adequate amount of thermal paste on the CPU. Before insertion, pull up all the posts one at a time and turn them clockwise at the upper end. Then align and insert the tip of all four semi white sleeves into the holes, making sure they are inserted correctly by checking the other side of the motherboard. Once in, just push the diagonal posts 2 at a time until the black centre pins lock them into place. Plug in the fan, then double check again then all four posts are locked correctly.

kalohimal wrote on 2020-08-28, 00:01:

Sounds like the HSF might not be mounted correctly. You might want to take a look at the bottom of the motherboard and make sure that all four pins of the HSF are inserted correctly. They each has a semi white colour sleeve that is split into two halfs and a black centre pin at the center. Be careful when inserting the semi white sleeves as they could bend and break easily. The way to properly release them is to turn the back knobs counter clockwise, then pull up all the way. Good practice is to release 2 diagonal posts first, follow by the other 2 diagonal posts. To reassemble, first remember to apply adequate amount of thermal paste. Before insertion first pull up all the posts one at a time and turn them clockwise at the upper end. Then align and insert the tip of all four semi white sleeves into the holes, making sure they are inserted correctly by checking the other side of the motherboard. Once in, just push the diagonal posts 2 at a time until they lock into place. Plug in the fan, then double check again then all four posts are locked correctly.

I'll double check the pins when I get a chance. It's also possible that I didn't use enough thermal paste.

If I have to take the cooler off anyway, I'd kind of prefer to just go ahead and install the other CPU and cooler, as I had already planned to do after making sure the motherboard was working.

What I'm wondering, though, is how confident I can be that things are in good enough shape now that I'm not risking damage to the new CPU? The power connector thing kinda spooked me a little, so I want to be careful about how I proceed.

Btw, I managed to get a picture of the POST screen in the split second before it went blank, and OCRed the text:

AMI BIOS (C) 2006 American Megatrends, Inc.
ASUS P5PE-VM ACPI BIOS Revision 1501
CPU: Intel(R) Pentium(R) 4 CPU 3.20GHz
Speed : 3.20 GHz

Press F8 for BBS POPUP
DDR Frequency 400 Mhz, Single-Channel or Virtual Single-Channel
Checking NVRAM..
504 MB OK (Installed Memory Size:512MB)

Auto-detecting USB Mass Storage Devices ..
00 USB mass storage devices found and configured.

Keyboard/Interface Error
NO Keyboard Detected!
CMOS Settings Wrong
CMOS Date/Time Not Set
Press F1 to Run SETUP
Press F2 to load default values and continue

I did also try it with a USB keyboard attached (before I took the picture), but it still went blank after a split second, and I still wasn't able to get to the BIOS setup screen.

I would not keep powering it on without checking the HSF, as repeated overheating might damage the CPU, even though it has built in thermal protection (overheating the CPU while voltage is applied could cause electro migration which would damage the traces on the die). There is a slight chance that the earlier incident of plugging in the wrong power connector might damage the VRMs, on the board but I think it is unlikely, as the voltage is lower than its original +12V and one rail is shorted to ground, causing PSU's short circuit protection to kick in and not start. The current issue is most probably just pure overheating of the CPU. Also note that you don't need excessive thermal paste, just enough to have it spread a thin layer over the contacted area would be ok.

kalohimal wrote on 2020-08-28, 00:47:

I would not keep powering it on without checking the HSF, as repeated overheating might damage the CPU, even though it has built in thermal protection (overheating the CPU while voltage is applied could cause electro migration which would damage the traces on the die). There is a slight chance that the earlier incident of plugging in the wrong power connector might damage the VRMs, on the board but I think it is unlikely, as the voltage is lower than its original +12V and one rail is shorted to ground, causing PSU's short circuit protection to kick in and not start. The current issue is most probably just pure overheating of the CPU. Also note that you don't need excessive thermal paste, just enough to have it spread a thin layer over the contacted area would be ok.

Ok, thanks! So it should be safe to go ahead and swap out the CPU and cooler, then? The new CPU doesn't run as hot as the one currently installed (Core 2 Extreme X6800 @ 75W TDP vs. Pentium 4 HT 541 @ 82W TDP), and the new cooler (Scythe Big Shuriken 3) should be better than the Intel stock cooler that's in there right now.

Yeah you can, but need to make sure that the BIOS is up to date to support the newer Core 2 CPU. According to Asus website, the Core 2 Extreme X6800 requires BIOS version 0604 or later and yours is 1501 so it should be fine. Core 2 CPUs can also be slowed down a lot better than P4 for DOS games.

Can you try using a known good PSU? I wouldn't trust that PSU with oddly colored power connectors.

EDIT: I realized he used the 4 pin extension form the ATX connector in the 12V CPU connector, so nothing odd about the colors, my bad.

There's nothing odd about them.

Please unplug wrong plug by the CPU then, find the loose 4 or 8 pin connector that does have wires in black and yellow then plug that in instead! That is for the CPU 12V supply. The one you plugged in is for the ATX motherboard's power connector.

Cheers,

Y'all, I appreciate you wanting to help, but the wrong-4-pin-connector problem has already been resolved, earlier in the thread.

The current problem is that the screen goes blank a split second after POST, and I get a beep code indicating "CPU Fan Error or CPU Over Temperature Error or CPU Over Voltage Error".

As far as I can tell, the stock CPU cooler is seated properly, although it's possible the thermal paste isn't distributed enough (thick paste + low-pressure cooler), so I'm going to try installing a different CPU and a different cooler today (I was planning on swapping them out anyway, so nbd). That is, unless anyone chimes in with a reason why I shouldn't do that.

EDIT: Btw, since one of you mentioned using a different PSU - I was actually thinking about doing that, since the current one is just the cheap one that came with the case. But all the name-brand PSUs I've been looking at all seem to have all-black cables, which concerns me a bit given my earlier mistake. Do the ones with all-black cables at least have clearly-labeled connectors?

Also, any specific recommendations for good-but-affordable PSUs? I don't think the wattage needs to be particularly high - the case's PSU is only 350W, and I had calculated that as being sufficient.

That cpu doesn’t heat up that fast more likely that beep isn’t a overheat and it’s the fan sense. So u a either have a bad fan B your fan is plugged in Wong fan header C your fan plug is wired different than the pin out of the fan header D that beep inst a fan beep

Warlord wrote on 2020-08-28, 20:43:

That cpu doesn’t heat up that fast more likely that beep isn’t a overheat and it’s the fan sense. So u a either have a bad fan B your fan is plugged in Wong fan header C your fan plug is wired different than the pin out of the fan header D that beep inst a fan beep

Ok, so all the more reason to try switching it out for another one, right?

Ya try just another fan or check the wires

Warlord wrote on 2020-08-28, 20:43:

...
D that beep inst a fan beep

I had considered the possibility that I was mishearing three beeps as four, but three beeps means "An anomaly is detected in the graphic card. If the graphic card needs an extra power supply, please ensure the power supply can provide enough wattage".

I don't have a graphics card installed right now, though. I have the monitor cable plugged into the motherboard's VGA port, so it should be using the 865G chipset's built-in graphics, yeah?

Ya I think it’s probably not onboard vga. A fan can be trouble shooted tho you should check the wired are not pulled out under the sticker