You seriously need outer hard drive, steam games are pretty fast to reinstall, so I think those would be your best options, left 4 dead or anything!
Check out CCleaner for hidden waste files you have, deleted me alot waste stuff and longer the computer has been used, more likely there is alot stuff left behind! Remove all waste stuff with cleaner and just clean whole registry but remember to save the back-up file for first time!
http://www.ccleaner.com/download (don't get cheated by the donation asking links, its free!)