Windows 7: Random hang/ freeze (Ctrl+Alt+Delete and mouse cursor not responding)

I start getting this problem about 3 days ago.
Frequently happen and it annoy me all the time.
Sometimes, it happen (5 minutes or 10 minutes after startup) and sometimes not (I leave my desktop idleing for 10 hours straight, but no freeze happen).
Please don't say I need to clean reinstall my desktop as I have around 50 games installed and I don't want to lose them.
I appreciate every reply you give

There is a couple problem that this can occur.

1) The OS system file is corrupt, then you may need to run it.
2) Some driver is not up-to-date.
3) Bad sector on HD disk.

From your description, you should go to command prompt and do this first.

start > accessories, right-click "run as administrator". At command prompt, type "sfc /scannow". It will try to analyze your OS files and see if it can recover it. Try do it two times. If you get no result... try check for hard disk bad sector.

Go to My Computer, right-click on your main HD (OS C and choose "Property". Go to Tool tab, and choose "Check now". Check both options. click Schedule now. Restart computer. it will check for bad sector and remove bad file. Should be able to fix your problem.