Please post the rest of your specs so we can get an idea of what we're working with.
As far as what to try... here's what I'd start with:
Check Event Viewer when the freezes happen to see if there's any clues.
Try updating all of your drivers from each component manufacturer.
Monitor your temps with something like HWMonitor.
You could also try running a chkdsk on your drive to make sure it's alright. Open up a command prompt as admin (if on Vista/7/8), and type in: chkdsk c: /f /r
It will ask to run on next reboot. Type Y and press Enter and then reboot your computer.
You could also check your RAM with Memtest86+: Memtest86+ - Advanced Memory Diagnostic Tool
Burn the ISO to a disc with something like IMGBurn, and run it for a minimum of 4 hours (overnight is usually best).