Lets see how it works in safe mode
Download and make a full updated scan with malwarebytes
Follow the clean boot procedure (although probably similar to what you did, we cannot take a chance to rule out the true cause) http://support.microsoft.com/kb/929135
Check memory with memtest86
Make sure that you are not over heating.
Try in safe mode; report back if it works properly.
Try a clean boot
Make sure PSU is working properly
If overclocking, restore to original
Test hard drive at company website.
Check back and I will get you some links that you can use for the above http://www.geekstogo.com/forum/topic...ing-memtest86/ http://support.microsoft.com/kb/929135 http://malwarebytes.org/ http://www.almico.com/speedfan.php
Almost forgot. Type event viewer, in search (by start button) and look for errors that may show the cause of the problem.
Go into event viewer and look for critical errors relating to the problem
You want to look for critical errors (they have red in the left column ).
When you find them you want to look for critical errors that say app hang, app crash, or anything that relates to the problem.
This seems like a lot, but go slow, ask questiions and you will be up and running