Sometimes apps become unresponsive or don't perform as intended. In those circumstances, it is a good first step to close, or force quit the application to ensure it is no longer running. Upon reopening, the application may have been restored to working order by the restart.
If these steps don't work, you may need to reboot your computer.
Directions for Closing or Force Quitting
Students - Wharton Computing Student Support
Faculty - Academic Computing Services
Staff - Administrative Support