My brother's PC failed on him. It had worked fine for 2-3 years with an Athlon 1700 processor.

At first we thought it was a dodgy disk drive then found the noise was actually the PC speaker vibrating. Fault-finding, we removed all boards except AGP and disconnected all drives - same result. No keyboard lights and no screen display, although the CPU fan worked OK.

Noticing the Northbridge fan had seized we assumed it had been fried, although the system isn't overclocked at all, and decided to replace the motherboard. We did this tonight, using a PC Chips M848ALU.

The PC speaker remained quiet and the CPU fan ran, but everything else remained dead. No keyboard lights, no POST beeps, no monitor signal, nada. We also tried with an old monitor adaptor card instead of the AGP in case it was that, but no dice.

This seems to exonerate the Mobo. The only two things left are the PSU and the CPU and I don't know enough to be able to decide which one is more likely - or maybe there's something else I'm overlooking.

Can anyone suggest what the likely cause of this is, or advise if there's any way to decide the culprit given that we don't have any spare PSU or CPUs to try swapping?

Replying to myself, in the hope that it may help someone else later down the line ...

The problem was the PSU, not the CPU or Motherboard. Looks like before it failed completely it managed to cause some disk corruption though.

So my brother is down the cost of a new motherboard AND a new PSU. But now he has on-board ethernet and USB 2.0, which he didn't have before as well as an upgrade path.

(Wanders off, whistling "Always look on the bright side of life").

Did the PSU take out the Mainboard when it blew?