Have Dell Optiplex 790 imaged with Windows 7 Interprise 64-bit. Need two graphics cards to support 3/4 monitors. The Dell came with one card - tried adding a second card identical to the one already installed by Dell. Crash occurs after driver update takes place and a restart. Process works fine with the same machine and 32-bit version of Windows Enterprise. ??? Have also tried using the VisionTek X1550 card - same problem. Thanks in advnace.