Problem with Gigabyte 8800GT

Hey guys,

I need your help! My fairly strong and new pc was off for 3 months while I was on vacation. I came back and turned it on. I worked on it for about half an hour until it suddenly shut itself down. I opened the case, finding my 8800GT's heat sink burning hot. I let it cool for the night and tried finding the problem on the following day. I tried turning the pc on but the fans only rotated for a fracture of a second before it shut down again (the pc never got the POST). This time the temperature was normal, nothing even warm. My findings were that the card's hardware is okay (the fan works), the PSU and everything else is all working but the problem depicted above occurs when the power connector on the card is connected to the PSU (either to the PCIE power connector or via the PCIE power connector adapter supplied by the manufacturer so that rules out a faulty PCIE power connector from the PSU). When I disconnect the power connector and let the card operate solely on its PCIE slot power, the system boots perfectly.
Anyone has a clue about this issue? I have no one to turn to as the store I bought the system from when bankrupt. Is it okay to operate the card without its PCIE direct PSU power connection?

Thanks a lot.