Hi All
I was battling with this problem for 2 days solid and worked out the solution.
If you have done an upgrade from windows vista and the computer freezes when shutting down/logging off/restarting it is a problem with roaming profiles.
To repair this remove the computer from the domain and make it a workgruop computer. Restart wait for it to restart even if it takes long.
Your problem should then be resolved.
Try rejoin domain once all has been resolved and you are confident that it is shutting down properly.
reply to this thread if you need any more help on this issue