OK, so we tried switching out the ram sticks, one at a time. Nothing happened. Then I tried, a spare PSU, and the computer worked. Power LED is green, and the four lights, at the back, are all green, except for the one that says D. It's orange. On the screen it shows the following:
Diskette drive 0 seek failure
Performing automatic IDE configuration...
Drive 0: Disk Drive
Drive 4: CD-ROM Device
Drive 5: CD-ROM Device
Strike the F1 key to continue, F2 to run the setup utility
So I'm guessing, he needs a new PSU.