I had a similar problem - I have almost exactly the same hardware as you down to the graphics card. However it wasn't my graphics card that blew, it was my lovely 24" Dell monitor. Almost a week after I set up the maximizer to use 2 screens, it pooped out. Of course I used that "opportunity" to buy myself 2-22" monitors as a replacement. I didn't alt-tab; I simply used two windows on the same screen. Warranty had expired too :-(

Now I have 1 character per monitor & things seem to be working fine for now.