|Hmm, this sounds either like a virus or overheating issue|
My advice would be to check for latest antivirus definitions and perform a FULL system scan and see if anything comes up
Other than that, just check that the CPU heatsink is installed correctly. Use software like hwmonitor (free) to make sure that none of the components are getting too hot (most websites reccomend that your model of CPU should not go above 75'C)
Hope that this advice helps!
Edit: Just re-reading your post you should try using memtest86+ which will scan your memory and test for errors.