may not be the gpu but the power supply may not be holding up the 12v line. see if you have another video card...cheap one that uses less power then the card you have. also try one dimm of ram and unplug the harddrive from power to see if you can keep the mb power up in the bios.
Thanks for the answer, ive tried removing Harddrive and also use only one dimm ram but the same things happen.
Actually i can get into bios but then the screen just goes black.
I hope it was gpu, ill try find another gpu and will check it out.