Have a desktop PC (Core i7, DDR3 RAM, Gigbyte motherboard, ATI 4850 graphics card, Windows Vista, Coolermaster case, hooked up to a GNR 19" flatcreen monitor).
Boot up machine into Windows Vista no problems, after roughly about four-five mins, feed to monitor goes, monitor signalling 'no signal'. Machine seems to continues to run, fans, hard drive activity etc. Nothing seems to bring the monitor signal back except for rebooting. Reboots back into Windows, rinse and repeat. No software or hardware conflicts visible in system settings. I popped the case to see if the graphics card had become unseated, appears ok.