Two things I've found very useful for me as far as increasing my computer productivity:
1) Set my homepage to a one where it says in big letters "DON'T PROCRASTINATE". Like this one that I made for myself:
http://www.alexanderkharlamov.com/dont-procrastinate/
2) Delete all the bookmarks to time-wasting sites. Be RUTHLESS
. If you make it so it's an effort to remember the URL and then type it, eventually you'll stop going to that site.