Hey .. I've had this problem for a while and I tried the best I can on my own to solve it .. but I really couldn't .. so I need some help .
When I play a game .. after a while it completely locks up my computer .... and I see vertical purple and green LINES covering the screen ... and I have to RESTART .
This happens with games like BATMAN Arkham Asylum and Tales of monkey island .. and as you can see these two games couldn't be more different from each other ( in terms of graphics and SYSTEM requirements I mean ) . so I think the problem isn't my VGA card ... so does anyone have any thoughts about this .
My system specs are : VGA card Nvidia 9600 GT .
4 GB RAM
Core 2 Duo 2.8GHZ processor.
Windows & operating system .

Thanks for your help in advance .

Actually, that's usually a sign of a video problem.

Some things to check:
1. Make sure the video card is securely seated in the slot.*
2. Make sure both ends of the video cable are securely connected.*
3. Make sure the video card's fan and heat sink(s) are clear of DUST.**
4. Check for dust build-up on other components while you're at it.**
5. Check your computer temperatures with a program like Speedfan.
6. If you have on-board video, switch to it and see if the same thing occurs.
7. If possibly, try your video card in another computer, or try another video card in yours.*

* Unplug the computer before doing this.
** Unplug the computer before doing this. Use a can of compressed air for cleaning. Do not vacuum!
Last time I saw vertical purple and green lines covering the screen it was when my graphic card did not get enough whit power to keep the fan spinning, and seconds later I was in a store buying a new graphic card and more power supply.

So make sure it's not to hot in there and check for dust and crap in your computer. Check the list what quaxo posted and see if it worksit seems that its a complete video card problem
i had the same problem

ive changed the video card now