Hey there... one of my characters can't login to any game.. he gets failed to connect all the time... what the hell do i do?

Log out & close D2

Try Deleting "Bnetcache" from ur D2 folder & relog into D2

You may have experienced a roll back in which case you are "flagged" and may get fail to join for 15-20 minutes.

The last time you were in a game with your character did it say connection interrupted?

Wait 20 min or do what cobra said.