first off do you have all the power plug plugged into the video card?? if you did check to see if the mb or video card is presssing down on the mb shield and shorting out. with new mb check to see there no dirt or bent pin in the pci slot. if your mb has two video card slots try the video card in another slot.
when i have it plugged in is when i have the black screen problems. Right now the gpu is plugged into the mortherboard and everything is working fine, so i dont think the mobo is shorting out. I already looked over the graphics card and the mobo to see if i saw anything broken and it didnt appear to have any broken parts. I will try the other slot now though