OpenSSH tunnel and connect to MySQL
Try checking:
Connection > SSH > Protocol options > Don't start a shell or command at all.
You also have a local and remote port of the tunnel swapped (You have 2 and 3 labeled other way around.)
It should be:
L3307 => 127.0.0.1:3306
Check PuTTY event log for details (PuTTY console window title and select "Event log").