Time required: Two minutes.
Prerequisites:
1. Your account name and password. (deleting "steam\config" wipes your stored account credentials)
2. Access to the email your steam account is tied to. (you'll need the SteamGuard auth code)
Instructions:
1. Close steam (Right click steam icon in system tray > exit)
2. Navigate to your steam folder (usually "C:\Program Files (x86)\Steam")
3. Delete or move the folder called "config"
4. Start Steam.
5. Log on to your account.
6. Play.