Is the freeze truly random, or does it happen under certain circumstances, such as when the system is under load (e.g. while gaming)?
There's not a lot of information there. Could be malware / droneware, overheating, RAM, PSU, GPU, etc. etc....
While gaming yes but also sometimes just on the desktop, it's random, my pc has been on 8 hours and froze 3 times, twice in wow and once on desktop. It's not malware or anythink like that, systems clean.
did you just upgrade something or change a setting?
think really hard.
what was the last software you installed, the last software you updated, the last driver you updated/installed the last hardware you installed..
did the problems start after these?
and make sure your pc is cool. try powering it with two power supplies. that's worked for me a few times.
Download RivaTuner v2.05. And check the GPU and CPU temps. It is important that you read the manual. It will make it easier to access the settings and you can damage your card if you make changes in the wrong area.
Looking at the spec's, the voltage might need to be at 2.2 volts. If your bios is set for auto, it could be giving it only 1.8 volts. Also running memtest for at least 4 to 6 hours to make sure it is stable.
I would still get rid of the PSU. Maybe you could pick up a meter and check the power at one of the molex connectors while under load. A junk PSU can damage HDDs. Two bad drives seems a little suspect.