I had this problem with my really really stupid Fujitsu Simense Esprimo Mobile V5545... which is a crap model I can assure you.. sometimes, the laptop just freezes and strange colors appear at the monitor, and slowly goes into black..
I noticed that this happens more when viewing videos online, sometimes while playing video games, and some times without any reason, it just freezes..
I had a XP Profissional operationg system, I faced the problem there lots of time, until one time, the system files got corrupted, and XP wouldn't load, I lost everything..
Now I have vista, and I face the same problem.. it's frustrating.. the laptop had the problem since I first bought it (September last year).. it's a matter of time until the system crashes...
Please tell me what can be done.. apart from sending it to the Fujitsu service.. as I need the laptop and repairing it will take forever, that if it works at all..
P.S. Don't you ever buy a Fujitsu Siemens Notebook, they are the worst..