Originally Posted by radix
To summarize, it could be the power supply, the motherboard, the graphics card, the ram, or the hard drive.
We're so helpful it hurts.
Hard drive? No. You'd still see the BIOS screens on the monitor.
Graphics card? No. You'd hear the POST beep.
RAM? Probably not.
Motherboard? My guess.
PSU? Also a possibility, if one voltage died, you'd still see some lights.