Connecting to SQL 2005 Database Engine

I've installed an instance of SQL 2005 on Windows 2000 Server and cannot connect to the database engine locally. If I try to connect to the instance through management studio, it refuses to acknowledge that the service is even running. I've checked the database engine is running, browser and agent. All the services are running, I've tried restarting them all but it doesn't work. Can't figure out why I can't even see the database server locally. I'm logged in with an admin account.

I did install service pack 4, not sure if SP4 is supported under 2000 or not, I don't think it is. Would that mess anything up? It seemed to install fine. I've installed 2005 on 2000 Server machines before and had no problem connecting locally. But the server was also a domain controller. Shouldn't make any difference should it? I don't think it's a credentials problem, I can't even see SQL Server.