Sudden restarts of my computer

Since a number of weeks I get automatic restarts of my computer which sometimes succeed and sometimes fail (left with a black screen).
I think it was after I changed from Norton to Panda antivirus but I am not totally sure.
I also changed to a new sound driver during that time I think.
Restarts occur at random times, just after powerup till after a number of hours. Restarts always occur when the trial time is up when we are playing the Midtown madness2 trial. It seems to occur more when playing games.

I also get error dumps 0x0000001e and 0x0000008e.
According to microsoft I have either a driver problem or a memory problem. I run the memory checking utility they recommend but no problems were found.
Websites I consulted pointed in the direction of the haxdoor virus but no references were found using panda or online scanners (Kapersky)

I ran all of the sticky thread however the AVG antispyware did not succeed, it just disappeared during running after checking approx. 164.000 items when it is busy checking the registry. I tried a number of times.

Thanks in advance for your help.