I would reset your BIOS settings to default by removing the battery and jumpering the CLR CMOS pins for 5 seconds. Replace jumper and battery.
See if the problem still occurs with the BIOS at default. If you are not OC'd and your case has good ventilation, overheating shouldn't be an issue with that processor. Unless it's faulty.
Then clean your system of resource wasting crap and registry errors with CCleaner. Do the CLean and Defrag both.http://www.piriform.com/ccleaner