Sometimes, even the simple solution to restoring working backups in iTunes doesn't work. In that case, the ultimate fix is to perform a restore on your iOS device. The biggest drawback about this is that you'll loose all the saved settings, apps and their data, and you'll potentially be forced to start setting up your iOS device all over again, so use this tip as a last resort in restoring your iOS device to working order again. Here are the instructions for performing a restore in iTunes:
Connect your iOS device to your computer and launch iTunes if it doesn't do so automatically. Allow it to perform a sync, and once it is completed click on your iOS device's icon in the left most pane in the iTunes window.
You'll see something like this:
Locate the Restore button on the summary tab and click it. You will be prompted by iTunes to start the restore. Once it is completed, you'll have factory fresh firmware loaded onto your iOS device. Eventually, iTunes may prompt you to complete the restore using the most recent backup. If you do so, you'll be able to restore some of your old apps, data, and settings.
Compatibility: iPhone, iPod touch, and iPad.
