Impossible PC boot (stucked at q-code 94)

Biscottoman · 25 Apr 2022 at 16:20

Hi guys I have a pretty serious PC problem so I hope some of you can help me. A few days ago during a shutdown Windows hangs on shutdown by switching to a black screen that leads the PC to a loop of blank reboots terminated by a direct shutdown of the PC using the power button. Subsequently, the PC was no longer able to boot, not even reaching the BIOS, the boot phase stopped with the motherboard with q-code 94 corresponding to the "PCI Bus enumeration" phase and the VGA led lit and then the boot retries automatically without ever reaching the BIOS and showing no video signal at all. Last night, two days passed (after trying various cmos, reboots and removal of power to discharge the capacitors) the PC randomly boots and resets a Windows error. Everything works perfectly (tested with cinebench r23, Crystal diskmark and some games) and even turning off and on again no problem of fate. After hours of use, convinced that everything had been resolved, I turn off the PC again and Windows freezes in the same way, bringing the PC back to its previous state. Today I tried for 6-7 hours to overcome this continous boot loop with constant code 94 and no video signal on the screen, but i wasn't able ti solve it and I have no idea how yesterday the PC managed to post. I suspect or a software problem of corruption of the BIOS due in some way to Windows or some hardware problem of the motherboard maybe, even if in my opinion the problem is really illogical and difficult to understand and appeared suddenly. Right now I have tried to remove the battery of the mobo, tried a boot without the main nvme which contains windows, tried to update the bios using the flashback usb port, but I have not tried yet to move the video card to other slots or such solutions as the system is cooled by a fairly complex double custom loop which takes time to take apart.
If anyone is able to help me I would be really grateful.

PS: we are talking about a really high-end rig (5950x, Asus dark Hero, 3090, ax1600i) each component cooled with custom loop

Tetras · 25 Apr 2022 at 16:39

The description of the Windows problems made me think of the boot SSD, especially the error when it booted, but faulty SSDs don't normally prevent the PC from having a video output, more likely they just disappear from the system.

BIOS corruption would be way down my list of possibilities, I'd suggest you don't try to update the BIOS again while it is so unstable (otherwise you might brick the board).

How much memory are you using?

Have you had any issues prior to the bad shutdown?

What peripherals and external devices do you have?

Biscottoman · 25 Apr 2022 at 16:50

I'm using two sticks of 16gbs of ram, which i haven't still tried to move since they are watercooled too (bad idea tbh), before the bad shutdown i didn't have any particular issue (the only thing some day before i've found the system restarted as I left it switched on while i was doing other things, still don't think it's a psu issue but probably the restart was caused by windows), i don't have external devices or peripherals (just mouse+keyboard and ofc monitor). The thing that i really can't understand it's how it managed to boot two days ago after two days of shut down and everything worked perfecly as I said (games, cinebnech score), the only things was that it restored something of the operative system. Some people told me it could have been cause by the "fast boot" bios option combined to a bad update of windows which could be fixed using the classic sfc/scannow+restore, but if it caused bios corruption i don't know how can i be able to boot again like two days ago.

Tetras · 25 Apr 2022 at 17:34

Biscottoman said:
I'm using two sticks of 16gbs of ram, which i haven't still tried to move since they are watercooled too (bad idea tbh), before the bad shutdown i didn't have any particular issue (the only thing some day before i've found the system restarted as I left it switched on while i was doing other things, still don't think it's a psu issue but probably the restart was caused by windows), i don't have external devices or peripherals (just mouse+keyboard and ofc monitor). The thing that i really can't understand it's how it managed to boot two days ago after two days of shut down and everything worked perfecly as I said (games, cinebnech score), the only things was that it restored something of the operative system. Some people told me it could have been cause by the "fast boot" bios option combined to a bad update of windows which could be fixed using the classic sfc/scannow+restore, but if it caused bios corruption i don't know how can i be able to boot again like two days ago.

A bad update of Windows would cause problems once you reach the point Windows is supposed to load, but it shouldn't prevent the PC from booting up at all (i.e. at least to the BIOS screen should work).

Having to use sfc/scan now to fix Windows installs is something I'd only expect if the SSD is corrupt due to bad ssd, bad memory or unstable overclocks of CPU / memory.

Windows updates very rarely touch the BIOS (I've only ever heard of it with microcode updates due to security vulnerabilities), so BIOS corruption is very unlikely. I would only suggest that if you had a bad/partial flash. No harm in pulling the battery for longer to make sure the settings are put back.

Intermittent boot problems are usually: memory, motherboard, PSU, in that order (either faulty, not fully seated or config problems), but I'm not confident enough to suggest anything.

As much as it will be unpleasant, I think you might have to take the watercooling apart here, or at the very least start re-seating components (like graphics card and memory) to make sure it isn't one of those silly intermittent things.

Biscottoman · 25 Apr 2022 at 17:55

Tetras said:
As much as it will be unpleasant, I think you might have to take the watercooling apart here, or at the very least start re-seating components (like graphics card and memory) to make sure it isn't one of those silly intermittent things.

yes, at the moment I'm organizing my work commitments just to find a day as soon as possible in which to calmly empty and disassemble both the loops so that I can test the various components individually, looking on the internet the most likely responsible components are the ssd or the gpu, even if I still can not understand how these managed to work without problems few days ago when the pc was mysteriously capable of boot and the related problems showing up only during the shutdown process

Tetras · 25 Apr 2022 at 18:07

Biscottoman said:
yes, at the moment I'm organizing my work commitments just to find a day as soon as possible in which to calmly empty and disassemble both the loops so that I can test the various components individually, looking on the internet the most likely responsible components are the ssd or the gpu, even if I still can not understand how these managed to work without problems few days ago when the pc was mysteriously capable of boot and the related problems showing up only during the shutdown process

Yeah, it is hard to say, but components that are loosely seated, or having a slow death can be like that, off and on.

Biscottoman · 25 Apr 2022 at 18:15

Tetras said:
Yeah, it is hard to say, but components that are loosely seated, or having a slow death can be like that, off and on.

If something has to be faulty I just don't hope it hasn't to be cpu or ram since tbh, also in case I would fail to solve by testing ram, nvme and gpu in different configurations; is there any way i could figure out for sure if the cause is the motherboard rather than the cpu or vice versa?

therealdippy · 26 Apr 2022 at 13:06

Since it managed to boot into OS once after the issue first occurred I am more inclined to suspect hardware. Whilst a BIOS corruption is possible, it's not likely to cause pcie issues one day and not the next. Based on the evidence it looks like the GPU enumeration fails and so re-seating the graphics card could be a good idea.

Hagar · 4 May 2022 at 06:48

Q code 94 may be the last successful stage and the one following it is the one falling over. Just something to check out. What are they in the manual?

Biscottoman · 6 May 2022 at 13:04

Update, i've just tried reseating both nvme, mounted the GPU on the second pcie slot, tried a 780 ti insteaad of the 3090 and I'm still unable to boot (still stucked to q-code 94). So clearly not a gpu issue or something, dunno how to proceed now...

Haz123 · 6 May 2022 at 14:28

Hopefully you have another PC around so you can test that the 3090 is working ok. If the gpu is ok then I would say the motherboard is the most likely faulty component.

I know it is going to be a real pain but stripping it down and testing each component individually is the only way to be certain what is faulty. If you could get into the BIOS i would say reflash it but I would not advise you try via the flashback button on the back.

Just cpu + ram + any old gpu should allow you to get into the BIOS , if you cannot get there then you have a baseline to proceed from and thats RMA Mobo or CPU with the first being most likely dead product.

Biscottoman · 6 May 2022 at 14:33

Haz123 said:
Hopefully you have another PC around so you can test that the 3090 is working ok. If the gpu is ok then I would say the motherboard is the most likely faulty component.

I know it is going to be a real pain but stripping it down and testing each component individually is the only way to be certain what is faulty. If you could get into the BIOS i would say reflash it but I would not advise you try via the flashback button on the back.

Just cpu + ram + any old gpu should allow you to get into the BIOS , if you cannot get there then you have a baseline to proceed from and thats RMA Mobo or CPU with the first being most likely dead product.

I really suspect the motherboard too, the only issue is that i don't have any way to test the CPU individually to be 100% sure, surely now I'm going to take apart the second loop to remove RAM waterblock and test each bank individually but after that i'm totally lost (i can try a different psu too or just different power cables, but honestly i don't think it that this can be the fix)

Haz123 · 6 May 2022 at 14:41

My mobo died just before xmas and I had to strip the loop as well , it is a real pain. If you do try a different PSU then make sure you use the correct cables , do not mix and match powercables from different suppliers unless you are absolutely certain they are the compatable.

Biscottoman · 6 May 2022 at 14:46

Haz123 said:
My mobo died just before xmas and I had to strip the loop as well , it is a real pain. If you do try a different PSU then make sure you use the correct cables , do not mix and match powercables from different suppliers unless you are absolutely certain they are the compatable.

I would have used the other cables the ax1600i provides. At the moment if something has to be faulty i really hope for the motherboard, in my case it's the easiest ti rma and and i have worked a lot to found the best overclock settings for my RAM and CPU

Biscottoman · 6 May 2022 at 17:17

Just tried to reseat the RAM into the other slots, still same issue