I don't know what happened, but for the past few days, I cannot join any public CS:S server. The server list refreshes, but after I pick a server to play, the console displays "Connecting to server...". After five seconds, I get an error message "Connection failed after 4 tries."
I tried many servers, but I got the same message. When I play a LAN game, everything is fine.
I can't figure out what's wrong.
[EDIT]: It seems like a lot of people are having this problem after the Steam Update on Dec. 23rd. It happens with HL2DM as well as DoD:S servers. There doesn't seem to be a real solution yet. I think this is yet another Valve's bugs that was introduced with the rushed updates.