The recent problems with displaying the server list within Half-Life has been identified as a load related problem with the Half-Life Master Server. Valve has provided a temporary fix to the master server to prevent this problem from occurring. This temporary fix limits the maximum number of servers that will be returned to the Half-Life client. Currently this limit is set to approximately 2000 servers. If your favorite server is no longer showing up within the Half-Life client, please add it directly to your favorites list to gain access.

Valve will be addressing this problem in upcoming update for Half-Life and the update will eliminate the need for the limit of returned servers.