Firtst of all, if any overclock, turn down.
Second thing you should do after a thorough malware/spyware/virusscan and the problems are ongoing:
http://www.memtest.org/
(do a longtime run, speaking about 1-2 hours)
After that (if no errors) check compy voltages, CPU,GPU,PSU andcase temps
http://www.softpedia.com/get/System/...-Edition.shtml
And do a HD check.
If all looks good, try a live Linux (Ubuntu) boot CD, don't be afraid, nothing is changed on your HD, but it as Ubu does a syscheck when booting it can point to eventual hardware problems.
Also: try to lower the CPU MHZ a notch, same for your RAM/GPU
If all fails, hehe, a fresh install can do wonders.
And stay away from pron sites.