I have a PC that died tonight after I swapped a power supply. Putting the old power supply back did not help.
Symptoms: Fans and lights come on normally. There are no beeps, but I don't see any speakers on the motherboard and I don't remember if it beeped in the past. The monitor stays in no-signal low power mode.
Significantly, the front panel power switch will turn the PC off. I believe this switch requires CPU intervention to work properly, so that indicates the motherboard and CPU are working properly - or am I missing something?