I can't imagine it would be a PSU issue, from memory the 5800 cards will use more power than a 660, it's also a quality PSU.
Have you tried the card in a different pcie slot?
Failing this I would try a new m/b, a pretty drastic step but I think the card and hard drive have been tried in different systems so you know they work ok.
Have you tried the card in a different pcie slot?
Failing this I would try a new m/b, a pretty drastic step but I think the card and hard drive have been tried in different systems so you know they work ok.


