ok...I tried everything you told me.. At first I tried to install windows and I got an error "can't find a hard disk". Then I did a memory test using Ubuntu installation cd. Everything seemed to be ok as far as ram is concerned. I installed ubuntu, everything was working properly till I decided to make an upgrade. Pc then turned off by its own, and everytime I try to get into Linux, again screen has some weird colors and pc does nothing after a while. Any more suggestions? Might it be a hard disk problem?