Ran CCleaner and did nothing. It freezes after leaving it idle for 15 minutes, and sooner if I ran a game or process, like moving stuff to EHD.
Please list your system components. In the meantime, you may want to check to see if one of your system memory sticks has failed. Download the .ISO file and burn yourself a Memtest CD: http://www.memtest.org/
Boot to the CD with a single stick of memory in the first slot. Let the pgm run for at least 1 FULL pass. If no errors, switch out the stick(s) and run again. If any errors at all show up, that stick is bad.