If you have not done so already, I would run a test on the RAM to see if any of it is giving errors. You can run memtest86+ or I believe Windows 7 has one that you can run as well. Run the test for a few hours to see if any errors are returned. If there are errors, this is a sign that some of the RAM is bad and would have to be replaced. Bad RAM can cause freezing, stuttering, blue screens, and random reboots so it is always a good idea to test it first.