Says im logged in somewhere else

Whenever i try to join a gmod server it says im logged in somewhere else and need to log in again, ive tried doing that and restarting steam several times and its still the same. There is no problems when im playing other steam games like css or tf2, so my question is if anyone else has had this problem and maybe have a solution?

Instead of restarting, log out and back in.

Or… exit Steam, then ctrl + alt + del and under processes, end hl2 and steam. Then try logging in.

Change your password, somebody might know it and be using your account.