[masraum]

What ^ he said. Reboot it.

And yes, you can "kill" apps without rebooting as well. double press the main button. That should bring up a list of the running apps at the bottom of the screen. Press and hold one of the apps that you don't need to be running. After a couple of seconds, they'll display a small "do not enter" sign and start to wiggle. Click the do not enter sign to kill the app.