Got another PC for repair.
This one stopped working after a sudden power failure.
Specs are:
CPU: AMD Sempron (unknown, was too lazy to take the heatsink off), Socket 754
MB: ASRock KBNF4G-SATA2 (Or K8BNF4) (nForce, with built in GF6100 GPU)
HDD: Excelstor 80GB IDE
PSU: Codegen 300W

Totally stone dead, no beeps (even without RAM). Fans run, but nothing more.
Tried clearing CMOS, swapping PSUs, tried running with only RAM & CPU (& built in VGA) but the system remained totally dead.
Probably the crappy Codegen PSU did not like the sudden power failure or maybe a power surge went through it and killed something on the board. The PSU still works through, voltages seem to be in spec.

Another system bites the dust. Good for parts only.