If your computer is going slowly, especially on the internet, you may want to clean out your cache files. These 'temporary internet files' are saved on your computer anytime you visit a web site. They will contain pictures and graphics from sites you have visited. If they accumulate they can slow down your computer considerably.
If you run anti virus software, these often contain a feature to clean out your temporary internet files. However, I am not convinced that they always do the job. Potentially those programs could be pointing to the wrong folder or only deleting certain files.
Cleaning your cache is fairly quick. On Internet Explorer:
Tools > Internet Options > General Tab > Delete Files Then click on the box for 'Delete all offline content' Then click OK and OK
You should see your computer start to go a little faster.
The steps for other browsers should be similar. Check the help files for details.
If you are really curious, you can click on Settings then View Files to see all the junk that is sitting on your computer.