Hey guys... i'm pretty scared right now because I think my mobo is fried.
I bought this computer just over a month ago and to go with it I chose a cheaply 8600GT for 50 euros... I decided I would OC the crap out of it until it fried, cause on my nexty paycheck I would buy a decent GPU. About a week ago I started getting crashes / freezes whenever I entered 3D apps (games) and I thought the card was finally dying... so today I was browsing for new GPUs and I caught sight of a 8600GTS for only 45 euros... so I thought "what the hell, it's faster than my GT and I can buy a better GPU in a couple of months again anyway"... so I bought it and happily replaced it with my dead 8600GT.
Or so I thought.
Just to be careful I decided not to OC this new card... but to my surprise.. the same thing happens.. I get crashes / currupt graphics / text, etc. And if I don't if I don't Alt-Tab to desktop right away, it will crash and only a reboot will do it. This is exactly what happened with my previous GPU.
I ruled out coincidence because they are 2 different GPUs, from 2 different brands. The older one is from ASUS, this new one is from XFX.
I imediately thought of mobo problems... turns out it my 8600GT wasn't dead after all... could it be that the OC could damage the PCI-E slot / mobo? :X
If an Alt-Tab to Desktop saves the crash, I'm thinking it might be a driver problem. Even though the cards are similar, did you thoroughly clean out the old drivers before you added the new card? If not, try doing that, then install the latest drivers for your card.