I bought the iPhone 3G and I've downloaded applications (legally) on the appstore.
Everything worked fine until I click on an application at random and the latter does not start.
The iPhone displays the entry screen of the application, and then automatically returns to the home screen.
What is the problem?
The problem comes from the protections of Apple Appstore accounts. Only the account used to download a particular apllication, will be valid . If you have two account this can be the cause of the problem.
This solution, requires no restauration