Same machine as the 'missing desktop' i recently posted about and managed to fix myself.

Now we're having hardware issues. No power whatsoever today when i tried to turn the beast on. Tried a spare power supply and now it comes on but stops during the POST at the memory check. Here's what I've tried:

Disconnect all hard disks and CD drives.
Remove, replace and swap RAM modules.
Tried two power supplies.

Specs as follows:

420w PSU (toast) - testing on spare 350w
ASUS M2NPV-MX mobo
AMD X2 5600+ CPU
2048 MB DDR2 800 RAM
Nvidia 8600 GT graphics card

Any ideas appreciated before it goes back to the shop!