Depending on the browser, for Chrome it's the settings tab, go to the bottom, "Show Advanced Settings", click that and then do the privacy tab to "Clear Browsing Data..." and then choose in the screen that comes up what things you need to delete, I do all but the bottom two things, and then select "Since the beginning of Time" and click "Clear Browsing Data".

In IE it's Internet Options, go there and then "Settings" And under Browsing History select "View Files" and then manually select them all and then hold Shift down and hit the Delete key on the keyboard. This will permanently delete something for you so it's not going into the 'Recycle bin' instead. As far as Fire Fox I don't use it much so I don't know, but the above directions for IE I bet will help you to figure it out.

Hope you get your computer woes worked out Mari! ♥