You could run a memory test to check. Download Memtest86+
(you want the 2nd one Download - Pre-Compiled Bootable ISO (.zip)
). Unzip it then create a CD from the iso file using your CD burning software. There is a good freeware burner called ImgBurn
which will do this easily.
burn the .iso file directly to CD. It must be used as input to a program that knows what to do with it, like the one I mentioned above.
Boot the CD and run for at least 3 complete passes unless it shows errors sooner than that. An overnight run is even better.