SRCDS on Windows 2k3?

I’ve never had a problem running SRCDS on my Windows Vista PC, but for some reason it just won’t work on my Windows 2k3 Server. I’ve forwarded all of my ports, but the game doesn’t show up as on the Internet or the LAN. I’m using the same server config file that I’ve been using on my Vista machine without problems. The last line printed in the console shows that the server is indeed up, and even connecting to Valve:
“Connection to Steam servers successful. VAC secure mode is activated.”

Check firewall.

I’m going to be installing 2k3 on my hosting machine soon. If you haven’t found your problem by the time I get it set up I’ll help you out.

Windows Server 2003 supports it just fine. I run all my steam servers off of that, a cluster of 3-4 win2003 boxes.

I have this PC on my router’s DMZ as well as redundant routing rules. Windows Firewall isn’t even enabled. That was my first idea, but I really have no idea what else could be causing this.

[editline]04:58PM[/editline]

Well, I just had the crazy idea to use the “connect” function in the console. I couldn’t connect through my external ip, but I could connect through the server’s internal ip. However, the server doesn’t show up in my LAN in the server list. There’s no reason it should be on my LAN…

[editline]05:25PM[/editline]

OK, I just fixed it. I’m not really sure what I did, but it worked. I just made sure of the standard stuff, sv_lan 0, heartbeat etc.
If anyone has experience with somewhat old computers, maybe you can help me here: http://www.facepunch.com/showthread.php?t=811202

Ugh… It worked once, but never again. I still don’t know what the problem is.