I just got a new Gigabyte 660 GTX OC. I have it plugged into my psu and my mobo, but when I plug it into my desktop my screen does not turn on. I have no dvi cables, but I used a vga-dvi cable to plug it into my monitor. I can use my computer normally if I plug my monitor into my mobo for using the integrated graphics chip. The GPU seems to be working as the fans are spinning, but It doesn't come up as registered hardware on my computer.