New 7800x3d build, motherboard standby light is on, but PC won't start

Hey guys!

Didn't know the best place to post this, so I thought I'd post it here. Just thought I'd pick a few brains since my new build won't boot and I can't figure out why for the life of me. I was assembling a PC with my son for his first gaming PC. I had a bunch of spare parts laying around, so all I needed was a CPU and a motherboard, so I bought a 7800x3D and an Asus ROG Strix B650-A on sale and threw it all together with him on the weekend.

Currently my issue is the motherboard standby lighting goes on when I plug it in, but I can't get the PC to start up. I've done the following troubleshooting steps:

1) Tested the PSU with a power supply tester to confirm power is being supplied via the 24-pin motherboard and 8-pin CPU lines. Tested fine.
2) Disconnected panel IO from the motherboard and attempted to start via shorting the power switch pins to confirm the issue isn't with the case power button.
3) Two different individual RAM sticks in slot A2, one and a time, to rule out any RAM issues.
4) Confirmed nothing shorting out the back of the board.
5) Cleared CMOS.
6) Updated BIOS via BIOS flashback.
7) All power cables are tight and locked in.
8) RAM sticks are locked down.

Not sure if I'm missing anything, but nothing seems to turn this PC on. Anyone have any ideas?

Thanks for the help!

Try removing the gpu and using onboard graphics to start up.

learners permit said:

Try removing the gpu and using onboard graphics to start up.

Click to expand...

Tried it, but the problem is that it won’t power on at all, so I don’t think that would be connected. I get standby power to the board, I just can’t get the system to turn on.

Some motherboards won't turn on if a CPU cooler isn't installed (if one of the CPU/pump headers is not used) as a protection measure.

The last troubleshooting step that I'd take before starting to RMA components is to remove the motherboard from the case and test it on a nonconductive surface. This will rule out a short from the case or an errant screw behind the motherboard.

that^^ make sure your cpu fan is connected right and if it is, then rip it all apart and try firing up just the board with it on the mobo box.

Do the fans startup?

• Sometimes it does start up, but the monitor you're connected to doesn't display the BIOS, especially for certain monitors (older monitors, portable monitors, etc.). This was one head scratcher that got me once, I was troubleshooting for hours.
• Sometimes it helps to use slower RAM. I don't know what RAM you're using, but if you're using something like 8000MHz, you might have trouble starting up. Try something like a 5600MHz stick.

Hey guys!

Well, don't know what happened, but I eventually got it to start up from the test bench, after previously failing to get it started from the test bench. In any case, it's fine now. I wish I had an explanation, but I really don't.

Thanks to everyone who dropped some suggestions!

I had a similar experience about 15 years ago and removing the board from the case allowed it to start up after some fiddling. Put it back in the case and bam no start up. Removed again and it started up again. Found one of the mother board stand offs had a really sharp burr on it where the lead thread on the stand off would perforate the masking of the pcb and short the top layer of the pcb to ground. Found it by rubbing my index finger across the top of every stand off until I felt a needle sharp point that would jab into the board and when the screw was tightened it would poke through the masking and ground the pcb layer.