same thing happened to me things were fine dandy then one day server list comes up empty after haveing the game installed for almoast a month without any problems. thats why im looking in these forums.
Occasionally GameSpy has problems and you'll get that.. but the list should return eventually. If it remains an issue... I'd look at your firewall or router.
I use Gameranger, it just came out for PC. See I sometimes have this trouble with JA and Gameranger picks up the servers for me. You should try it out.