Crash problem with my Geforce 8800 GT Alpha Dog

Hi guys.

I've recently upgraded my PC with a new Motherboard, Chip, Windows 7 etc. Ever since, I've been having problems with black screen crashing.

When this happens, the PC is still on, music still playing etc, but just nothing getting through to the monitor.
This immediately made me think of a Graphics card problem, but the weird thing is, it hardly ever crashes unless I use Windows Live Messenger or Windows Live Mail. When I use either of these it tends to crash right away.

The drivers are up to date, and after searching for any vaguely related problems on various forums I also tried disabling the desktop window session manager, ran a System File Checker, updated the Network adaptor drivers, and turned off the power saver. Nothing has made a difference.

So, I bought a cheap pci graphics card (ATI 3D Rage II) and tried that. The picture and everything was horrible but the crashes stopped for the whole day yesterday. But there's no way I could live with that card long term.

I put the Geforce 8800 GT back in, and for a few hours last night and this morning no crash problem. Then, bang, starts crashing again, and is now back to crashing everytime I open Windows Live Messenger or Mail.

The card worked fine in my old PC, although I never used it for gaming or anything else too demanding. The one time I attempted to play Pro Evo 2009 it would crash, but I always put that down the having a very basic mobo, chip and ram.

The card was bought 2nd hand off ebay as a gift for me. It's always been very loud.

So, have a got a faulty card, or is there something I can do to rescue the situation other than shell out for a new card?

Any advice would be gratefully received, but my PC knowledge is pretty limited so please go easy on me!

Cheers,
Mat...

My spec is:

Abit IP35 Pro XE Motherboard
Intel Q6600 G0 stepping
Geforce 8800 GT Alpha Dog Edition
E-Mu 1820M soundcard
Corsair 650W PSU
4GB Crucial Ballistix RAM
Windows 7 Home Premium
Medion MD7477 LCD Monitor