Updated from Ubuntu 13.10 to 14.04. When you go to "Shutdown", the only 2 options are "Lock" and "Log off". There is no option to "Shutdown". Have to use sudo shutdown -h now command. The option from the Shutdown > shutdown worked the first 2 days. After that the above experience. Thanks in advance for your help.

it depends on the GUI I think (do you have gnome, or unity, or ?). Probably you need to log off and afterward you can shut down the machine.

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Do you start X manually or log in via a display manager? In case of latter use a different "session" to login, or in the case of the former try prefixing "dbus-launch" to your .xinitrc for the entry that starts your DE, or use startx instead of xinit.

I would like to thank everyone for their helpful suggestions.
A few points for clarification. I am using Ubuntu 14.04 ( 64 bit ) with Unity. I followed the suggestion to log off. Initially that did not solve the problem. I still had to shutdown using the terminal. When I rebooted and then went to the shutdown and it again took me to "log out", which I choose, then going back up to "Shutdown" and clicking on that option, I was able to get the screen "Reboot" or "Shutdown". Since then, the computer is behaving as it did after the initial install. Thanks again.