If you didn't read the original thread, my problem is that when I play games in fullscreen(for example CoD: MW2) I crash after about 15 minutes of gameplay with a bluescreen, or if I'm lucky the game freezes while I am still able to alt tab to desktop and close the application before I crash. When the "lucky" scenario happens I briefly see a tooltip coming from one of the icons in the lower right corner(probably amd catalyst) saying that the display driver stopped working... also during the "lucky" scenario, if I alt tab back into the game before closing it I get a blue screen.
I had the latest drivers but was told to roll back to 12.1, and I was not sure about the CAP so I didn't download any, I have 2 Radeon HD 5870s in crossfire. Since the downgrade of drivers I crash less.
I would definitely take a look at crossfire and 2nd card. In windowed mode, where you don't have an issue, crossfire is disabled. Once in fullscreen, crossfire is enabled, and problems start. That leads me to believe your 2nd card isn't working properly.