When you restore your Zune device software, the startup partition and the data partition are removed and rebuilt. In addition to removing the Zune device software, this process also erases all content, including music, videos, pictures, podcasts, friends, games, and audio books that are stored on the Zune device.
Warning To restore the Zune device software, you must have a Windows-based computer that has an Internet connection. That computer must have the Zune software installed. And you must be able to connect the Zune device to a USB port on that computer by using a Zune Sync Cable. Do not perform the following steps if you do not have any one or more of these things immediately available.
After you start to restore the Zune device software, you cannot again use the device until you complete all the steps. You will not receive any confirmation or warning on the Zune device after you start the following procedure.
To restore the Zune device software, follow these steps:
http://support.microsoft.com/kb/927001/?sd=zune