If your machine boots normally, then hangs when it tries to mount resources automatically, most likely one or more servers are down. Use init to go to single user mode or to a init state that does not mount remote resources automatically. Then start the appropriate daemons in the background and use the mount command to mount each resource usually mounted automatically through the /etc/vfstab file. By mounting resources one at a time, you can determine which server is down. To restart a server that is down or hung, see ``Clearing server problems''.
If you cannot mount any of your resources, most likely your network connection is bad.