put your mouse over the tab at the bottom and RIGHT click. END PROGRAM. if that doesnt work, rebooting may. if that doenst work, its probably a bug or a virus and I would scan your machine.

SuperAntispyware.com (free!) does a great job and is fast
Malwarebytes.com (free) also does a good job.
microsoft security essentials (free) from microsoft.com also does a good job and runs quietly and quickly in the background.
Many folks like AVG.com (search for the FREE edition)

good luck.