I forget where I have post something similar about that usual problem.
Anyway ... by any chance, did you have a personal firewall on your box ?
In that case, you have to check if you have UDP traffic out to
monster.idsoftware.com:27950 (
192.246.40.56:27950).
It is the main master server where Quake 3 requests to get public dedicated servers.
Dunno if you have a way (or know how) to check it ... but at least, it is the very last thing you can do