Many forget laptops need cleaning too. EXAMPLE at http://forums.cnet.com/5208-19681_102-0.html?messageID=3196452&tag=forums06;posts#3196452
The symptom sounds like an overheated video system. If the laptop didn't get its yearly cleaning the odds of needing this and more maintenance increased to a certainty.
I've had this Dell XPS laptop for 3 years. In the middle of web browsing today, the screen suddenly became unstable - everything on screen started to quake as if they were on a conveying belt. I can still read and work but very uncomfortably. The colors are all off. On a solid color background, waves of all colors show up like crazy stock charts. I tried restart computers a few times but the problem seems to stay. Any help please? Thanks.