I'm having a similar problem after updating to 10.5.4 from 10.5.1. Everything ran smoothly for about a day and then I found I was locked out.
Not working:
SSH, Server Admin (remote), Screen Sharing, ARD, FTP, VNC, Mail, probably other services too.
Working:
WGM, Web server
I had my host reboot with the power button and then I was able to connect with VNC and enter my localadmin id and pw in the server's login window. The login window went away and it just hung on the login background screen. (Now VNC just hangs without opening a window.) Then tried to connect with SSH and eventually got this message:
"Operation could not be completed: An unexpected error occurred (error code -10810)"
That message happened only the first time. Since then SSH times out with this message:
Keith-Kavanaughs-Computer:~ keith$ ssh me@000.00.000.000 -v -v -v
OpenSSH_4.7p1, OpenSSL 0.9.7l 28 Sep 2006
debug1: Reading configuration data /etc/ssh_config
debug2: ssh_connect: needpriv 0
debug1: Connecting to bwd01.bauwau.com [216.23.180.214] port 22.
debug1: connect to address 216.23.180.214 port 22: Operation timed out
ssh: connect to host bwd01.bauwau.com port 22: Operation timed out
Server Admin and the other services that aren't working all just hang with no message or error.
For what it's worth, I scanned the ports that Apple says are open by default in the firewall and indeed they were except 626 (Serial Number Support). Maybe that's normal.
Another thing that may or may not be relevant: I used Disk Utility to duplicate the startup disk to a partition on an external drive before updating. When I did that it changed the name of the partition from Backup2 to Macintosh HD, which is the same as the startup volume. I noticed right after that in Server Admin > File Sharing that in the volumes list only the two external drive partitions were listed. Not the startup drive. It did show up in Disk Utility though.
I'm a designer trying to run a server so I'm learning and have just enough server knowledge to screw it up. Any help on a direction to look or even a way to get in and look at the logs would be helpful.