Hello, I just built a PC and am having difficulty with the video card. I installed my OS and some programs and everything was working fine, and then I went to play Team Fortress 2 and started having problems. For about the first 5 minutes everything looked great, and I was running about 70 fps, but then vertical lines started appearing on my screen, and after about 10 seconds my monitor stopped getting a signal. This seems odd because BEfore I played any games on this computer I ran the 3Dmark program which runs a series of very detailed graphical situations for about 10 minutes and the video card performed great. I restarted, and everything is still working fine, but I'm not going to try to play any other games until I figure out what is going on. I'm running windows vista ultimate, geforce 8800 gtx, 4gb ram, intel quad processor, an aftermarket heat sync, and a 700W power supply. Any help would be greatly appreciated!