You've tried a complete restart, too? I know that sounds obvious, but a lot of people just relaunch the app and assume everything will be ok, but it may be the OS that's causing the issue. Also, if you have a tablet connected, disconnect it, wait about ten-fifteen seconds and reconnect. If this doesn't work, can you come back with some details around your OS and machine, please? It's easier to help with that information on something like this.
... View more