ZuneInsider has a neat tip to clear your entire MP3 player. This could be useful for when you want to sell or buy a used player or when your attempt at converting “The Matrix” into the Zune format left a large unreadable chunk of data on your device that you can’t seem to get rid of (another post for another time).

1. Set the Hold switch to unlocked.
2. Press and hold the Back button  while you press the top of the Zune pad. When the Zune device begins to start, release the buttons.
3. Immediately after you release the buttons in step 2, press and hold the following combination of buttons, depending on your Zune model:
- If you have a Zune 4GB, Zune 8BG, Zune 16GB, Zune 80GB, or Zune 120 GB device, press and hold the Back button  while you press the Play/Pause button. Continue to hold these buttons until the Zune device restarts and you receive the following message:

Clearing contents. Please wait.
note: If you have a Zune 30GB, press and hold the Back button while you press the right side of the Zune pad and the center of the Zune pad. Continue to hold these buttons until the Zune device restarts and you receive the following message:

Clearing contents. Please wait.

link – ZuneInsider.com