Had my GF4 ti4200 oc'd on all day / all night - little did I know the fan was being obstructed by the crystal orb connection wires..
Just noticed loads of glitches on my screen and immediately shut down and cooled the GPU.
Switched back on to find more glitches and artifacts, display resetting every 2 secs.
Tried 10 mins later but wouldn't even get past POST.
Was about to go to order a new card, but..
decided to give the GPU core and all the transistor/resistor thingies a spit clean...
Seems to have fixed it!
How odd is that - gonna try my magical spit on my mates broken ti4400 and 4200s who had exactly the same prob !