Question : Problem: PC crashes colourfully when running graphical applications (eg. DirectX)

A long while back I swapped out my old graphics card for a new GeForce 8600 GT. It was an upgrade from an earlier GeForce, and quite a substantial leap from 256Mb to 1Gb. A problem which was noted early on was the crashing, but it's rather unusual in how it crashes because it will only do this once.

Firstly, I can run absolutely any desktop application which doesn't require DirectX without problems. Everything from web browsing and programming to viewing movies in Windows Media Player. However, games like Red Alert 3, City of Heroes or Final Fantasy XI (to name the most commonly used) crash after running them for a few minutes.

The crash itself makes the screen go psychadelic. Colours change into bright pinks and dark shades, with a very stark contrast, but still being able to make out the game running in the background. Leave it long enough under this and it will eventually display a Blue Screen of Death, but because of the 'artifacting' (similar to JPG) going on it's impossible to read the message.

However...

Shutting down the PC by holding the power button and then powering the system back on will allow me to then run the SAME applications without any crashing. Full functionality will continue until the system is, once again, powered down.

Because I can still use my PC, I've never really considered this a top priority, but it's finally gotten on my nerves enough to see if I can finally get it sorted. Hopefully some of the brilliant minds here can shed some light on this mysterious issue.

Answer : Problem: PC crashes colourfully when running graphical applications (eg. DirectX)

I'd run a dxdiag and under the display tab check things out by doing the tests located there.  if you can do those without crashing it should rule out DX and you can start looking at the card.  

I had a similar issue about 3 months back, I just swapped out my card and everything worked ok.  Once it got past 69 C the card would do the exact same thing.  It should've been able to run a lot hotter but something got messed up at the manufacturers I guess.