Trying to play some keys but don't get any response from your device? :(
If you're working on Chromebooks you have to go to SETTINGS in the studio, click MIDI Settings and choose the keyboard you're connecting in the menu that pops up.
If you have Mavericks OS (Mac OS 10.9) - that is probably the issue since there is a tiny little bug there. But don't worry, just disconnect your MIDI keyboard and connect it again. That should solve the problem! :)