Question PC build will power on fans but no motherboard lights and won’t power off

[Confoozled]

Hi, first time PC builder here so apologies if I’ve done something silly.

I’ve just assembled my PC and attempted to power it on. The fans all come on (both the case fans and the AIO radiator fans, along with their ARGB alighting, but I get no LEDs lighting on the motherboard (including thE QLEDs which are meant to help debug boot issues). Similarly no screen signal (My screen is plugged into the motherboard HDMI, and I have no separate GPU plugged in at the moment to keep things simple).

Oddly, whilst I can power on with the PC’s power button (on the case), I can only make the PC switch off by flicking the PSU power switch off. If I turn the PSU switch back on within a few seconds of powering off, the fans come straight back on, without having to press the PC power button. If instead I wait 30 seconds between powering off at the PSU and then back on again, the fans don’t then come back on until I hit the PC power button.

The fans are all plugged through the fan/argb controller hub that came with the Be Quiet cooler.

Things I’ve already tried:
- checking the processor is properly seated (no change)
- removing all the memory and powering up without it (no change)
- checked the ATX power connector is plugged into the motherboard firmly
- praying to the hardware gods!

Hardware setup:
MSI AB50GL PCIE5 850W PSU
Asus Tuf Gaming Motherboard B650-Plus
AMD 7900x
2 x M2 PCI 4 Crucial SSDs (4gb each). 1 of these is in M2 slot 1 (the PCI 5 compatible slot), and another is in M2 slot 2. Is it ok to use a PCI4 compatible M2 drive in a PCI 5 compatible slot? I think the slots are meant to be backwards compatible
Be Quiet! Pure Loop 2 FX AIO
2 x 16Gb Kingston Fury Renegade DD5 6400Mhz Dimms (in sockets A2 and B2 respectively when I started this testing process, but currently removed)
Montech AirX ARGB case

Any advice or suggestions for troubleshooting steps would be gratefully received. Please ask if you need more info.

***THANKYOU***

 

[Lutfij]

Welcome to the forums, newcomer!

2 x 16Gb Kingston Fury Renegade DD5 6400Mhz Dimms (in sockets 1 and 3 respectively when I started this testing process, but currently removed)
You mean slots labelled A2 and B2?

Did you inspect the CPU socket on the motherboard to see if there are any bent or broken pins? As for your AIO's installation, try and loosen the mounting pressure on the AIO and see if that helps get the system to POST.

 

[Darkbreeze]

First thing I'd do is TRIPLE check to make sure you have installed ALL of the wiring coming from the front panel power switch and I/O panel, correctly. It is very easy, especially if you are not experienced with making these connections, to make a mistake.

Or, even completely disconnect them ALL from the front, and do this, to eliminate the possibility that it IS something coming from the front panel or connected wrong.

How to Jump a Motherboard Without a PWR_SW Button

Today's guide shows how to jump a motherboard without connecting the PWR_SW header that goes to the case power button. -

www.gamersnexus.net

However, the fact that everything else lights up but the motherboard and QLEDs do not, suggests that this is a motherboard issue. It's certainly POSSIBLE for it to be a PSU issue, but it is far less likely. It COULD also be an issue of a bent pin on the motherboard CPU socket, but in that case I'd lean towards probably it wouldn't ONLY affect the motherboard LEDs and QLED lights. As Lutfij said, if nothing else I suggested turns up anything I'd definitely pull the CPU and make sure there are no bent pins on the board.

Yes, it is perfectly fine to use a Gen4 M.2 drive in a Gen5 slot.

 

[Confoozled]

Welcome to the forums, newcomer!

2 x 16Gb Kingston Fury Renegade DD5 6400Mhz Dimms (in sockets 1 and 3 respectively when I started this testing process, but currently removed)
You mean slots labelled A2 and B2?

Did you inspect the CPU socket on the motherboard to see if there are any bent or broken pins? As for your AIO's installation, try and loosen the mounting pressure on the AIO and see if that helps get the system to POST.

Thanks so much for taking the time to reply. Sorry I wasn’t very clear! I have tried in A2 and B2, and also have tried just 1 DIMM in A2, and even no DIMMs at all.

I’ve inspected the AM5 socket and all pins look good. I’ve also tried without the cooler fitted at all. All with no change.

 

[Darkbreeze]

Also, make sure you have TRIPLE checked EVERYTHING here:

"No POST", "system won't boot", and "no video output" troubleshooting checklist

"No POST", "system won't boot", and "no video output" troubleshooting checklist This checklist is a compilation of troubleshooting ideas from many forum members. It's very important to actually perform every step in the checklist if you want to effectively troubleshoot your problem. 1.Did you...

forums.tomshardware.com

 

[Confoozled]

First thing I'd do is TRIPLE check to make sure you have installed ALL of the wiring coming from the front panel power switch and I/O panel, correctly. It is very easy, especially if you are not experienced with making these connections, to make a mistake.

Or, even completely disconnect them ALL from the front, and do this, to eliminate the possibility that it IS something coming from the front panel or connected wrong.

How to Jump a Motherboard Without a PWR_SW Button

Today's guide shows how to jump a motherboard without connecting the PWR_SW header that goes to the case power button. -

www.gamersnexus.net

However, the fact that everything else lights up but the motherboard and QLEDs do not, suggests that this is a motherboard issue. It's certainly POSSIBLE for it to be a PSU issue, but it is far less likely. It COULD also be an issue of a bent pin on the motherboard CPU socket, but in that case I'd lean towards probably it wouldn't ONLY affect the motherboard LEDs and QLED lights. As Lutfij said, if nothing else I suggested turns up anything I'd definitely pull the CPU and make sure there are no bent pins on the board.

Yes, it is perfectly fine to use a Gen4 M.2 drive in a Gen5 slot.

So the front wiring looks good to me, as do the pins on the processor.

I think I’ve found the problem though. I’d plugged In the ATX power connector but not the CPU one, which is on the top left and I’d hidden it behind my AIO radiator! (Newb error!). I plugged that in and it now powers up the motherboard, gets stuff on screen, and will power off as expected when I press the case power button.

In addition to the 8 pin CPU power connector, there‘s a 4 pin one just to the left of it (extreme top left of the motherboard). I don’t think ai have any 4 pin connectors for my modula power supply. do you Know what that power connector is for, and whether it is essential?

Thanks

 

[Darkbreeze]

The extra 4 pin is generally only needed if you are running the very highest TDP processors OR doing some pretty substantial overclocking. Moderate overclocking and for most all processors, you really don't need it. And a lot of power supplies, especially older ones don't have any EPS connectors beyond the basic 4+4, but, yours does.

The thing is, there AREN'T any 4 pin EPS/CPU connectors. There are ONLY 4+4 connectors, but they are NOT "8 pin".

They are "4+4" and the connector is loosely held together in the center, sometimes not even that, and will easily snap apart to create two separate four pin connectors if you decide you want to go ahead and plug that extra one in, which won't hurt anything and could potentially help to avoid any problems with your 7900x if you are running with Precision boost overdrive (PBO) enabled in the BIOS which it USUALLY is by default.

 

[Confoozled]

The extra 4 pin is generally only needed if you are running the very highest TDP processors OR doing some pretty substantial overclocking. Moderate overclocking and for most all processors, you really don't need it. And a lot of power supplies, especially older ones don't have any EPS connectors beyond the basic 4+4, but, yours does.

The thing is, there AREN'T any 4 pin EPS/CPU connectors. There are ONLY 4+4 connectors, but they are NOT "8 pin".

They are "4+4" and the connector is loosely held together in the center, sometimes not even that, and will easily snap apart to create two separate four pin connectors if you decide you want to go ahead and plug that extra one in, which won't hurt anything and could potentially help to avoid any problems with your 7900x if you are running with Precision boost overdrive (PBO) enabled in the BIOS which it USUALLY is by default.

My cables are unfortunately not like that - they're 2 rows of 4 pins, but not separable. I guess I could order a 4 pin one from Amazon if needed though.

My PC is now booting fine when using the on board video. I can also boot with my Gigabyte 4070 card plugged into the PCI slot, but with it's 8/4+4 pin power connector not plugged in. In this configuration the RGB on the 4070 card lights up, but the card does nothing other than look pretty (not entirely unexpected, as it's only getting power from the bus at that point). Again, the built in motherboard video still works though like this. However, if I try plugging in the power connector to the 4070 card and powering up, it won't power on. Not only that, even if I then try to revert to where I was before, by unplugging the 4070's power (or even removing the card entirely), it STILL won't power on. At first I was worried I'd bricked the PC, but I did eventually manage to get it to power on again, by (I think!) unplugging the lead from the plug socket to the PSU, pressing the PC power button, then plugging the PSU back into the wall socket and pressing the PC power button again. I've repeated the whole thing twice, plugging the graphics card back in to the bus but not power, booted fine again, and then shutting down and trying again, this time with the power connector to the graphics card. Again, exactly the same thing happened.

Any ideas? Does this maybe mean I need that extra 4 pin power connected to the motherboard if I'm going to be using the 4070? (I'm not overclocking, just using stock 7900x at default config). Or maybe some BIOS problem? Or a duff PCI slot or motherboard perhaps?

It's super frustrating as the PC is lovely and quick in office apps, but runs like a dog in games with the on board graphics as you might expect.

 

[Darkbreeze]

Yes they are. ALL "8 pin EPS" connectors are "separable". All. There are NONE that are not. It's a mandatory standard. There are NO exceptions to that rule that I am aware of. Not now, and not since like at the least, 14 years ago.

 

[Darkbreeze]

Yes they are. ALL "8 pin EPS" connectors are "separable". All. There are NONE that are not. It's a mandatory standard. There are NO exceptions to that rule that I am aware of. Not now, and not since like at the least, 14 years ago.

They can't even get rated as compliant if they are not and yours is brand new with the very latest features and connectors, so there is absolutely ZERO chance that it is not. ZERO.