strange freezs need help

today I was on works typing a letter and my everything froze...to the point I could not restart by using centra alt del. The picture got really strange and froze and had to hit the reset button. Thought maybe it was heat but then I turned on the ac and was in daytrading software scanning charts and bam happened again. Had to hit reset. Now this machine has 3 monitors 2 on a radeon 8500 le and 1 on a ati 7000pci and has been stable well over a year. I had charts on all 3 monitors like I always do and when it did freeze the picture got funky it was on the primary but at the same time was not able to drag anything on the other 2. Any ideas? Powersupply seems fine. If one video card is crapping out would it affect the other one?