First of all, thanks for all the responses.
Originally posted by MicroBell
Also consider testing this outside of the PC case on a workbench in case of a short on the board. Do you get any beep codes?
No beep codes. It doesn't start the boot process. That's the weird thing about it: if it was trying to start, failing and beeping, I'd be able to diagnose the problem (loose video card, incorrect ram setup etc). It doesn't even try. I think this removes any chance of it being ram-related: wouldn't it try
to boot even if it didn't find any ram? As in, the fans of the PSU would start to go round, maybe the cpu fan would kick in... none of these things are happening. I've tried re-seating everything except the cpu, and I'm loath to do that because it requires removing the psu (nasty thermaltake fansink with it's bloody huge clip), and I've seen enough cracked Athlon cpu dies already...
let me guess, the faulty PSU was a cheapo generic one?
Yes, and it's precisely for this reason that I myself spent nearly £100 on my own PC's PSU. Sadly the computer I'm working with had a cheap "hiper" PSU.
I will probably take the hardware out and test it outside the case, as suggested. It'll all have to come out anyway, I'm pretty sure there's nothing more I can do. If it doesn't work outside the case then I'll get a new mobo. Thanks again for all the advice.