I am not sure but may have a similar problem.  Have 3 user accounts, all with administrator privileges.  If I attempt to log off from one of them (the first one created) , windows begines to log off that user (#1)  and then hangs up part way and nothing else can be done on the pc by anyone.  Machine must be manually shut off.

 

However I can switch users to one of the other users, go to task manager and log off user #1 with no problem.

 

Any ideas.