memory card problems

Hi everybody, I just bought a new memory card from KINGSTON. It is a 512 MB DDR Value Ram. THe problem that I have is that my computer closes down when I am playing or even when I am in the internet. It reinitiates. As a matter of fact as I was writing a previous message the computer turned off by itself and it started again. I have not idea what could it be.
I have a Compaq 6020US
Service Pack 2
1.6 AMD anthlon
256MB orginal computer RAM plus the 512 MB DDR new memory card from KINGSTON.
I am using XP edition
First I thought that it was the microsoft spyware, trying to block the game, but I unblocked it and I still have the same problem.
Any suggestions?? :4-dontkno