hanging problem

It could be because your system is overheating.

Shutdown then unplug the system
Use a vaccum cleaner and suck out/clean out all openings on the outside of the case (including the bottom and fan output), do not bump or drop the PC as this could cause damage to the internal parts.
Put it back in place and start it up, if it does not hang any more, fixed for now.
Repeat every 3-6 monthes to prevent the over-heating problem.

If the above does not help, turn off power saving settings and screen saver. Mine are always set to never as I have found this may hang the system.

Check scheduled tasks, may have one that runs every 2 hours, this may appear to hang the system while the task is running (fastfind/virus scan).

You should scandisk and defrag at least monthly.

I ran into a problem like this a couple summers ago, Same OS, I spent hour after hour troubleshooting my problem, finally I got fed up and backed everything up and reformated. When I got everything installed again it was still hanging.

So what I am saying is if at all possible, I would do the same, it will save you hour of headache, and may fix the problem.

If it is Hardware take the following steps

If you have more than one stick of RAM then run with only one, if it still hangs, switch and put the other in.

Try running it with the case off, if it improves, then but does not go away try putting a fan close to your computer.

If still hanging, check the voltage running to the motherboard, make sure none of the voltages are high,

then I would look to your drive. If you are still hanging, download a drive diagnostic tool, your drive manufacturer should provide one on the website.

I would suspect it to be hardware, when it hangs once and a while then and not in any specific pattern then I could see it being software but if it freezes every 2 hours then I would say it is definatly hardware.

good luck