Question can update BIOS but can't turn on PC — why could this be?

[dwin03]

I need some help. I'm attempting to put together my new desktop PC (B650 AORUS ELITE AX mobo, Ryzen 7950X3D cpu, RX 7900 XTX gpu, 128GB ram, Corsair RM850X psu). I have it all put together on the motherboard, and when I performed the bios update over USB, it all seemed to turn on. but shorting the two power pins doesn't cause anything to happen and I can't turn it on at all. I don't think it's the motherboard because I turned the motherboard in for a new one when I had this problem a few days ago and I think the chances of two motherboards both being broken on arrival is pretty slim, so I was thinking it was maybe the PSU? but the paperclip test caused the PSU fan to turn on, so I don't think it's that either? On the other hand, plugging in the PSU and turning it on doesn't cause anything at all to light up on the mobo, so... I'm completely lost at what the problem could be.

 

[Bob.B]

I need some help. I'm attempting to put together my new desktop PC (B650 AORUS ELITE AX mobo, Ryzen 7950X3D cpu, RX 7900 XTX gpu, 128GB ram, Corsair RM850X psu). I have it all put together on the motherboard, and when I performed the bios update over USB, it all seemed to turn on. but shorting the two power pins doesn't cause anything to happen and I can't turn it on at all. I don't think it's the motherboard because I turned the motherboard in for a new one when I had this problem a few days ago and I think the chances of two motherboards both being broken on arrival is pretty slim, so I was thinking it was maybe the PSU? but the paperclip test caused the PSU fan to turn on, so I don't think it's that either? On the other hand, plugging in the PSU and turning it on doesn't cause anything at all to light up on the mobo, so... I'm completely lost at what the problem could be.

Make it smaller.
Remove the gpu.....test.
One stick of ram in slot b2....test.
Move the mobo out onto a piece of cardboard....test.

 

[Misgar]

Presumably both (identical?) motherboards worked before you flashed the BIOS?

Did you install Windows or Linux on a disk drive before you flashed the BIOS?

Did you update the BIOS on both boards in exactly the same fashion?

Are you 100% certain you downloaded the correct BIOS file(s) on to the USB memory stick?

If you managed to flash the wrong file on to both mobos, it would explain why neither of them work.

 

[pete_101]

Did you flash the BIOS before putting in the CPU? If so, is the CPU and RAM installed now?

 

[Paperdoc]

When you ran the BIOS update process, was the entire system completely installed in the case, just as it is now? Or, did you do that before installing in the case?

 

[dwin03]

Make it smaller.
Remove the gpu.....test.
One stick of ram in slot b2....test.
Move the mobo out onto a piece of cardboard....test.

I've gone ahead and done all of this... still nothing.

 

[dwin03]

When you ran the BIOS update process, was the entire system completely installed in the case, just as it is now? Or, did you do that before installing in the case?

It's not in the case right now — I haven't put it in there yet.

 

[dwin03]

Presumably both (identical?) motherboards worked before you flashed the BIOS?

Did you install Windows or Linux on a disk drive before you flashed the BIOS?

Did you update the BIOS on both boards in exactly the same fashion?

Are you 100% certain you downloaded the correct BIOS file(s) on to the USB memory stick?

If you managed to flash the wrong file on to both mobos, it would explain why neither of them work.

No, neither motherboard worked before I flashed the BIOS. No OS has been installed to the storage. I updated the BIOS the same on both boards, and I'm fairly certain that I downloaded the right BIOS file (F8a at this link)

 

[Paperdoc]

OK, so you have the system assembled and supported on some surface, but NOT in the case. Question: supported on what? It MUST be non-conductive. The circuit board traces on the bottom of the mobo can short to ground (and to each other) if they are in contact with some conductive material. And it does not need to be highly conductive like metal. People doing this sort of thing used to use a DRY wooden board, hence calling this a "breadboard" process.

The symptoms suggest the mobo is getting no power. ONE way is if you have not made all the necessary connections. Besides the huge power connector form the PSU, normally there is also a smaller dedicated connector into a socket near the CPU chip for power to the CPU directly. Also commonly there is a connector into a video card IF you have such a card added into a PCIe slot.

Another way this can happen is if the cooling fan for the CPU chip is not connected correctly to the CPU_FAN header. It MUST be plugged in there. (OR, if you are using a liquid-cooling system with a pump on the CPU and fans on a rad, the PUMP normally must plug into the CPU_FAN header.) In addition to controlling the speed of the CPU cooing device, that header monitors the SPEED signal sent back to the mobo on header Pin #3. NO signal in understood to mean the fan has failed and there is NO cooling for the CPU. Most mobos will send out a prominent warning on the screen if this happens AND proceed to shut down everything to prevent possible catastrophic overheating of the CPU chip. MANY mobos also will NOT allow you to boot up if there is no immediate speed signal at the CPU_FAN header when power is turned on.

 

[dwin03]

OK, so you have the system assembled and supported on some surface, but NOT in the case. Question: supported on what? It MUST be non-conductive. The circuit board traces on the bottom of the mobo can short to ground (and to each other) if they are in contact with some conductive material. And it does not need to be highly conductive like metal. People doing this sort of thing used to use a DRY wooden board, hence calling this a "breadboard" process.

The symptoms suggest the mobo is getting no power. ONE way is if you have not made all the necessary connections. Besides the huge power connector form the PSU, normally there is also a smaller dedicated connector into a socket near the CPU chip for power to the CPU directly. Also commonly there is a connector into a video card IF you have such a card added into a PCIe slot.

Another way this can happen is if the cooling fan for the CPU chip is not connected correctly to the CPU_FAN header. It MUST be plugged in there. (OR, if you are using a liquid-cooling system with a pump on the CPU and fans on a rad, the PUMP normally must plug into the CPU_FAN header.) In addition to controlling the speed of the CPU cooing device, that header monitors the SPEED signal sent back to the mobo on header Pin #3. NO signal in understood to mean the fan has failed and there is NO cooling for the CPU. Most mobos will send out a prominent warning on the screen if this happens AND proceed to shut down everything to prevent possible catastrophic overheating of the CPU chip. MANY mobos also will NOT allow you to boot up if there is no immediate speed signal at the CPU_FAN header when power is turned on.

Apologies for the late reply, I was out of town. It is currently sitting on the box the motherboard came in.
The plug is in correctly for the CPU_FAN header. The fans are from the Noctua NH-U12A CPU cooler. I tried plugging it in with the included cord that allows for the header to power two fans, and I tried plugging in just one of the fans to see if that might be the issue. Still nothing. When I switch the PSU switch from O to —, the motherboard lights up very briefly, less than half a second. Then nothing.

I'll probably be taking it in to a PC repair shop on Wednesday (the earliest my schedule allows for) to see if they can figure it out, but if you have any suggestions in the meantime, I am all ears. (I don't mean that rudely, I am genuinely grateful for the help so far.)

 

[Paperdoc]

Your symptoms suggest there is a short circuit somewhere causing power to be shut off. That's why I suggested the issue of improper stand-offs in a case. But there certainly are other causes. One I know of happens with certain odd fans that have dual power supply connectors. But there are so may possibles I can't really tell you what IS the problem. I hope your repair shop can identify the issue.