Buildapc

EZ Debug LED: Debug LED indicators
These LEDs indicate the status of the motherboard.

• CPU - indicates CPU is not detected or fail.
• DRAM - indicates DRAM is not detected or fail.
• VGA - indicates GPU is not detected or fail.
• BOOT - indicates booting device is not detected or fail.

They're on the right side of the mobo next to the RAM slot, above the ATX power supply connector.
If the diagnostic LEDs aren't OK... check that the power supply cable (Big 24-pin, middle right edge) is fully seated.
Check that CPU power is connected (8-pin, top right)

Check for extra standoffs.
Try different output connectors on the GPU.
My Nvidia card displays the POST/BIOS on the rightmost used output connector, but I can't remember what my 10xx did. I think it was DVI, HDMI, then DP.
Anyway, might wanna use a single monitor until you figure this out and make sure it uses that input, had a weird monitor the outre day that would default to some random input even if it was unplugged.

"he says the case has preinstalled standoffs."

Yeah, but those standoffs aren't always installed in the correct positions. And can definitely cause a short. It's worth double checking. Every standoff needs a corresponding hole in the motherboard. If one doesn't, remove it.

I had this happen before in two different ways:

1. GPU power plug not in all the way, no GPU power, no fans, no display.
2. Older motherboard, new CPU, and the motherboard needed a BIOS upgrade before it would work on the newer chip. I had to borrow an older Athlon chip from the store to flash the motherboard. Worked great after that. Two separate incidents. If it can be broken, I've broken it.

When you say he upgraded to AM4, are we just talking new mobo? New CPU as well? If you have any other compatible known working hardware you can try to swap things around to narrow down where the fault lies (i.e. try swapping out just the PSU, or just the RAM, or just the GPU). In addition to what others said about the standoffs, you could test for those as an issue by removing everything from the case and doing a makeshift test bench on the mobo box if you still have it and see if it boots then. Could even just be a matter of needing to reseat some connection.

Like the others said, double check your connections. It's easy to accidentally not plug something in all the way. Also, an extra preinstalled standoff wouldn't be out of the question and I have had that happen, would be worth checking out as well. You didn't mention what power supply you are using. New/used? Older used? Can you test the power supply on another computer to help rule that out?

First, verify the CPU is installed correctly. Make sure the triangle on the CPU lines up with the one on the socket. Also verify all power cable are properly seated.

That cpu doesn't have integrated graphics, but if you try it without a GPU do you at least get a POST beep?

Do you know if the PSU is good?

I recognize that with the age of this post you've either figured it out or moved on but I'd still be curious about what happened next

Does the onboard video work without the card? I'm wondering if enough power is being delivered to the card. Pretty sure I've seen exactly this when I forgot to plug in the power cable.