Basically, your smartphone or tablet is a computer in a smaller box, and like every computer it also crashes, freezes or stops working at the worst times. What to do when this happens? Here are some tips for getting your device working again.

AndroidPIT
Force close an app
If an app simply crashes and doesn't work, you might think that clicking the start button will solve the problem. Unfortunately, it only takes you to homescreen and keeps the app running in the background. To force an application to close, there are a few methods.
V at Settings> Applications, look for the crashed app, click it and then Stop.