Occasional Boot Problems

ok here's the deal
every now and again im just cruisin on my comp when all of a sudden the picture drops out, so i turn off the comp and reboot but nothing happens, usually i hear a beep at boot up but no beep... and no picture, i disconnect the power for a while and only occasionaly it will boot up again then i have to reset all my CMOS settings, im not sure what is causing this problem, this happened earilier with my ATI X700 and now that card is stuffed, it wont work in any of my comps, now im running my 9600Pro and it still happens, so it might be the graphics card im not sure,

any ideas because i have no idea whats going on???