Hey TMO members and talksters...

I've been facing a weird problem, my PC Specs are here:

2B PW233 PSU 500W
Intel Core 2 Duo E7500
GIGABYTE Radeon HD 5770 1GB
Biostar G31 M7 TE

Problem:
Everything was working greatly until I switched on my PC that day, and it wouldn't boot. I thought that my past PSU unit (Digital (R) 450W) was faulty, so I changed it to a newer one (2B PW233 PSU 500W), but that did no good even. When my graphics card is only plugged in the PCIe slot, the computer boots fine and everything works normally, except the display which won't show, because the GPU is disconnected. When I connect the video card with the 6 pin power connector, then push the power button, the PC won't boot at all, and the PC fans rotate a very very very little degree and then stop a.k.a instantly stop, and the green light above the power button flashes green.

\Can somebody shed some light over my situation? I bought this card at a rather high price and I hope it isn't bricked.