Hi and Welcome to BC:
There are a lot of factors that may be involved here causing your computer to be slow or un-responsive. One problem may be infestation of malware. Also your hard drive may be close to being filled or may have bad sectors on it or even several fragmented files.
Read this link for ideas to help with this:http://www.bleepingcomputer.com/forums/t/87058/slow-computerbrowser-check-here-first;-it-may-not-be-malware/
One caution about registry cleaners like CCleaner(mentioned in the article), if you use it be VERY CAREFUL and make sure to set a restore point before using it. If you remove the wrong things you can cause severe problems with your computer. I don't recommend the use of it at all for that reason.
Edited by douglas martin, 09 May 2008 - 01:05 PM.