Recently acquired the Mac G5 version of the nVidia GeForce 6800 ultra for my G5 Dual 2.0. Ihave installed the card and when it starts up I get my cursor and a black screen and nothing else. It will boot the Leopard install disk and will boot if i hold down select key from start up (safe mode?) It worked fine with previous card ATI 9650. Please Help! Thank you!