Cleanly reinstalling Steam

If you are here because you want to fix a game problem, stop what you are doing and validate it. Validation does everything uninstalling does (except change your settings, which doesn't require reinstalling either) in a fraction of the time and with a fraction of the bandwidth.

If that doesn't apply then here is how to perform a proper, clean reinstall of Steam:

1. Write down your Steam Account name and password - you will need them to log back into Steam once you have reinstalled
2. Logout of Steam if you are able to do so
3. Exit Steam
4. Move "SteamApps" and "userdata" out of the Steam folder. These are the folders that hold your games and various local save files so you want to keep them!
5. If you are having problems with a specific game, delete its folder from SteamApps/<account>
6. Uninstall Steam via Add/Remove programs, if you can
7. Restart if prompted
8. Delete Steam folder if it still exists
9. Hit windows key + r ( run at the start menu ) and type regedit
10. Delete HKEY_CURRENT_USER\Software\Valve and HKEY_LOCAL_MACHINE\SOFTWARE\Valve (or HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Valve on 64-bit Windows)
11. Restart
12. Download and install a fresh copy of the Steam installer from http://www.steampowered.com/download/SteamInstall.msi
13. Run the installer
14. Exit Steam before you first login
15. Move your "SteamApps" and "userdata" folders back
16. Run Steam.