Unable to open any applications or shut down

Unable to open any applications or shut down

I'm using Ubuntu 12.04 LTS.
Recently, I've been having a problem where everything will be functioning
normally, and then I get the same string of problems:
1.) I can't open any new applications, or at least not by clicking on one
in my sidebar.
2.) I can go to the dropdown where I can select 'Shut Down' but I click on
it and nothing happens.
3.) Sometimes before everything stops functioning normally, I will go to
shut down and it will stall in the full screen terminal like thing which
it usually passes through when shutting down.
4.) In both cases 2 and 3, I am forced to resort to just powering off by
holding down power button.