Why upgrading iPhone from iOS 3 to iOS 5 displays USB and iTunes icons? I upgraded my iPhone from iOS 3 to iOS 5. It is now blocked: it shows a USB icon and the iTunes icon. How to proceed?
Start iTunes on your computer (ideally on the one you used to sync your iPhone with) and connect the iPhone via USB.

You will get an error message or number if there is something else amiss, but usually getting iTunes to do the download and then the restore will fix things up for you.