I have had them in two different systems. One is a Phenom II 955 with Asrock board and 4 gig of RAM. The other one is an i7 12 core with 24 gig RAM and EVGA high-end board. They disappear in that I lose the processing thread. In Device Manager, the card still shows up sometimes, sometimes it doesn't. Windows 7 64 bit OS on both systems. Usually it is the primary card that lets go. I thought maybe it was the monitor at firs but I have tried 4 different types of monitors.