I purchased the above mentioned desktop yesterday, it worked fine out of box for a few hours then I took out the oem gpu and psu, installed a evga gtx 660 and a rocketfish 550w psu from my old tower. Other than the horrible cramp the card makes inside, it will not allow the pc to post. (Repeating long beeps) I tried the stock gpu with my 550w and it worked fine. Could it be a power issue or maybe an issue with the amd mobo/gpu and the nvida card? I'm stuck!! Any thoughts?