Download windows memory dignostic Microsoft Online Crash Analysis
There is instructions on the page on how to burn it to cd & run the test
Its bootable so aftar u burn it to a cd put the cd in the drive & restart your pc & if your bios is set correct it should boot of the cd & run the test i would run it for about 2 hours if it finds a problem & you have 2 sticks of ram remove 1 & run the test again if it finds a problem again put the stick you pulled out back In & remove the other stick & run the test again
Post back on how you go aftar doing this,