Video Card Problem????? Maybe.......

Hi everyone, I've been having this problem with my computer that I can't figure out. I think its video card related but you be the judge. I have a dell xps 630 with Windows 7 64bit, dual core e8500,WD 600gb 7200rpm, WD 160gb 7200rpm, WD 1TB 7200 rpm, 8gigs of Memory, SLI setup with 2 Nividia 9800gt's and a dual screen setup. About a month ago both my screens would go black and I couldn't get the picture to come back up without a restart. Once you restart the computer it would be fine, then it would randomly do it again. Sometimes a hour later, sometimes 8 hours later. I rolled back the drivers, uninstall the video cards and reinstalled etc, windows repair, try a lot of things but nothing worked. So I took out the primary card and switch it with the secondary card. Well it sort of fixed it but kind of didn't. Now instead of the screen going black, Both screens will freeze and the background and icons will change to multiple colors. Now I will have to restart and everything will go back to normal, but there is a new symptom which makes me think it might not be the video cards after all. All my internet explorer passwords such as facebook, yahoo mail etc. will be erased. I will wake up in the morning and check my email and the screen will freeze within 30 mins of starting the computer but when I get home and start it, I can be on for 4 hours or more before it freezes. What do you think?

check in device manager the graphics irq addresses "no conflicts" is what you want to see.
another place to see is in windows task manage click the performance tab check cpu % and memory usage and available memory that is freely available for the os.