If its a one off I would just suggest closing everything down and rebooting.
If you really need to see whats running the only thing i can think of doing here (other than rebooting) is to load task manager (right click on the empty task bar and select "task manager") and end the explorer.exe process. Then if nothing re-appears select "file>new task" from the task manager menu and type "explorer.exe". This should let you see everything that is running.
Is this happening often?