Help with my new graphics card

I recently bought an alienware aurora r4 from a friend but without the graphics card, my friend had a nvidia gtx 780Ti in the computer, but now that I have the computer (with no graphics card) I bought one, I got an asus geforce gtx 660 2GB GDDR5. but when I put the card into the computer it beeps 6 times, I've looked into what the beeps mean and they suggest that theres a video card error, upon discovering this I took it back to my mates house and tried to fix it, we spent a good few hours trying to but it I have no idea where to look, when we put his graphics card in (the one he had in the computer before I bought it) it worked (he was using display port) and a picture showed, but when my card was in there was no picture (I was using the VGA port). not sure how to fix this and I was hoping that someone on here could help