Have an HD 6950 (old, I know, I am into old computers, and this is as new as I get) that runs fine in my Gigabyte GA-MA770T-UD3P board with a 600W PSU, but when I went to swap it out with a GeForce 660 on my ASUS M3N72-D board with a 700W PSU, machine comes on, post beep is heard, but no...