Amy,
Whenever posting questions on these forums, please give us as much information as possible about your computer. Depending on your issue, we might need the operating system, processor speed, amount of RAM installed, brand name of the computer, (if there is one), and any EXACT error messages you are receiving, and any other information you think might be helpful. The more information you give us, the better informed our answer will be.
In the meantime, have you cleaned out the computer of "junk" files and stopped some of the unnecessary start up programs. If not, try using the links below to get that done:
How To Shut Down Unnecessary Start Up Programs
How To Clean Unwanted Files From The Hard Drive
After following the above instructions, make sure to run Scandisk/Chkdsk and Defrag to optimize the hard drive.
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In addition, have you tried checking the computer for Spyware/Adware/parasites? Please use the free programs below to do that. After download and installing the first two, make sure to update them from within their user interface. The third program can simply be downloaded to your destkop, then run.:
Ad-Aware 6 Spyware Removal Tool
?Spybot Search & Destroy? Spyware Removal Tool
CWShredder Hijack Removal Tool
HOpe this helps and let us know more about your computer.
Grif
I have also experienced the PC Freezing thing.
It can get quite irritating.
It sometimes freezes before I get my password login screen, other times when on the internet, Microsoft Excel, explorer, outlook etc...
Have run virus scans, formatted and reloaded everything, nothing helps. if you have any suggestions, PLEASE let me know what I can do.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic