Troublshooting a server update

From Mac OS X Server FAQ

Suggestions for initial steps :

• Check the logs. Launch the Console application in the Utilities folder and click "Logs" icon in the upper-left to see a list of available logs to read. A good place to start is /var/log/install.log. Logs can be viewed remotely by SSHing into the server, and running the tail command: tail -n 500 /var/log/install.log | less (this shows the last 500 lines).
• Download and run the matching Combo updater version of any update you just applied, from http://search.info.apple.com/?search=Go&lr=lang_en&kword=&q=server%20combo
• Run the repair permissions routine using Disk Utility (you may need to do this from the Server Install CD). While this is no panacea, it can solve some problems, some of the time.
• Disconnect any extraneous hardware, if at all applicable.
• Check for third-party startup items or login items. Third-party startup items would live in /Library/StartupItems and login items are configured in System Preferences/Accounts. Temporarily disable anything that seems suspect. Startup Items can be disabled by moving the startup item's folder out of /Library/StartupItems. Login items (incorrectly called startup items by System Preferences) can be disabled by removing them from the list using the (-) button
• If you can't log in (using the GUI) after an update, you may need to remove two preference files. Startup in single-user mode (hold down  and s when you the machine starts up). Keep holding those keys until you see text information on screen, then type each of these lines, followed by a return:

mount -uw / rm /Library/Preferences/com.apple.loginwindow.plist rm /Library/Preferences/loginwindow.plist reboot