computer

If you have already cleared your browser's cache, cookies, history blah blah, then there's no going back. It's gone. If you are talking about deleted programs and documents, you can try an undelete program. See e.g. http://www.download.com/3120-20_4-0.html?tg=dl-20&qt=undelete&tag=srch . But if you have wiped your hard disk, or if the bytes have been over written, it would then be pretty much impossible. ;P