reinstallation always seems to work. if you play games with a lot of DLC, back up the game folders in the Steam/(your username) folder onto either a flash or Ext-HDD before you uninstall Steam and just place them back AFTER you reinstall Steam AND the game.
After reinstalling the games, pause ALL downloading, and then move the folder for the game from your backup into the same folder it came from. After that, restart Steam and it won't try to download what you previously had.