The turn off computer dialogue box appears in Safe Mode, but not in in regular boot when trying to shut down. I go to Start menu, click on Turn Off Computer, the dialogue box with the Hibernate, Standby, Turn Off, and Restart buttons does not appear and computer hangs up. How do I fix this?

I think it has been disabled.
See if this will help...

How to enable/ disable turn-off/ log-off option in start menu | computer (http://www.techpavan.com/2008/08/08/how-to-disable-enable-shutdown-logoff-start-menu/)

i think it has been disabled.
see if this will help....

How to enable/ disable turn-off/ log-off option in start menu | computer (http://www.techpavan.com/2008/08/08/how-to-disable-enable-shutdown-logoff-start-menu/)

This link dealt with the Start menu itself and not with the dialogue box that pops up in the middle of your desktop when you click on Turn Off Computer. That box has the buttons for Hibernate, Turn Off, Restart, and Log Off. Not sure where to find the option to turn it back on. Thanks.

Hmmm... then I'm stumped.
Now I want the answer... I'll keep digging.