Although not an easy option to consider, it is by far the safest, most effective one - Reinstalling the Windows OS. (Windows OS Install Disc Required)
You seem to be having problems with the computer and internet/browsing related problems, so a fresh lease of life can help you start over again. This time, be sure to carry out regular maintenance, install a good anti-virus and anti-spyware program, keep everything up-to-date.
(You can always backup the files you need, before you go ahead with this option)
On the other hand, if you are only referring to browser related problems, you might want to :
1. Reinstall Internet Explorer (uninstall ; download and install latest version)
2. Try resetting the Internet Explorer settings