Is this your PC?
http://support.packardbell.com/de/it...neymoon_imedia
If so, Via chipsets don't like the G92 based video cards (8800gt & gens 8800gts) and you'll probably need a bios update for the video card to make it a gen1 card (PCI-E 1.0) instead of a gen2 (PCI-E 2.0)
Other than that, I have to agree with Dai's assessment that your PSU is inadequate.