Either power supply or Motherboard, more likely the former than the latter. I had this exact same thing happen with an old eMachines unit I got for free. As Lutz mentioned, manufacturers cut costs wherever possible and power supplies are one of the first on the chopping block.

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth