So, I understand that you are getting standby power that lights the buttons and a few other LEDs. That usually indicates that the PSU is at least trying - no blown fuse.
The 2-digit POST display would read 00 for most CPU failures. When that display stays dark, power is not coming from the PSU, but it might not be the PSUs fault. Any short circuit could put the PSU into current limiting.
The next step is to remove storage components, video card and RAM one thing at a time. If the malfunction clears up, the one thing you removed is the likely cause.
Another test would be: With the PSU switched off, remove the CPU from its socket. Then switch on the PSU - the same LEDs as before should light up on standby power. Press the START button. A 00 POST code would correctly say that there is no CPU, but that's bad because the CPU was causing the problem.
Is the motherboard in a case? If so, the next step would be to remove the motherboard from the case and set it on the black inner box of the ASUS packaging - that's a good anti-static device for out-of-the-case testing. Look for anything that got under the motherboard and caused a short. With the CPU in and all other components disconnedted from mobo and power, connect 24- and 8-pin PSU cables and try to power on. BIOS POST progress up to memory steps would show correct operation. Correct operation outside the case means you are still looking for short circuits in the case, mobo mount or other components. Reinstall the RAM, reconnect the storage, reinstall the VGA, and try to power on -- all one at a time. If the malfunction returns at any point, you can tell which component caused it if the installations are done one at a time.
Swapping the PSU would be the next step. Since you're considering a new PSU ayway, this step might come earlier for you. If the malfunction continues with another PSU, its down to the CPU and/or motherboard. To tell which, you'd have to replace one or the other. The CPU might have failed to a short circuit which would overstress the motherboard VRM, so it might be both. I've had that happen on a M9A - the magic smoke got out of a VRM phase and the big brown scorch saved me the need to troubleshoot.
The 2-digit POST display would read 00 for most CPU failures. When that display stays dark, power is not coming from the PSU, but it might not be the PSUs fault. Any short circuit could put the PSU into current limiting.
The next step is to remove storage components, video card and RAM one thing at a time. If the malfunction clears up, the one thing you removed is the likely cause.
Another test would be: With the PSU switched off, remove the CPU from its socket. Then switch on the PSU - the same LEDs as before should light up on standby power. Press the START button. A 00 POST code would correctly say that there is no CPU, but that's bad because the CPU was causing the problem.
Is the motherboard in a case? If so, the next step would be to remove the motherboard from the case and set it on the black inner box of the ASUS packaging - that's a good anti-static device for out-of-the-case testing. Look for anything that got under the motherboard and caused a short. With the CPU in and all other components disconnedted from mobo and power, connect 24- and 8-pin PSU cables and try to power on. BIOS POST progress up to memory steps would show correct operation. Correct operation outside the case means you are still looking for short circuits in the case, mobo mount or other components. Reinstall the RAM, reconnect the storage, reinstall the VGA, and try to power on -- all one at a time. If the malfunction returns at any point, you can tell which component caused it if the installations are done one at a time.
Swapping the PSU would be the next step. Since you're considering a new PSU ayway, this step might come earlier for you. If the malfunction continues with another PSU, its down to the CPU and/or motherboard. To tell which, you'd have to replace one or the other. The CPU might have failed to a short circuit which would overstress the motherboard VRM, so it might be both. I've had that happen on a M9A - the magic smoke got out of a VRM phase and the big brown scorch saved me the need to troubleshoot.
