List all Components.
List all running processes.
What anti virus and Anti spyware programs are you running?
Have you added any new software or hardware latly?
Download everest or speedfan and list the tempartures and voltage readings it gives.
Go through this guide (Unless you already have)
Any additional information about what you use the computer for, things youve changed or added would be most helpful.
Google, download, burn and run memest86 for a few hours (6 Minimum) and report results.
You can also try reinstalling the Video Card Drivers.
Google, download and Follow the instructions of Driver Cleaner Pro.
Then reinstall latest Video Card Driver.