You can restore your Apple TV both on the unit itself and through iTunes. Choose Settings > General > Reset and click Restore to return your device to its factory-fresh state. If you can't make this happen directly, there's also iTunes. Make sure you have a micro USB cable on-hand (a lot of Bluetooth earpieces use this style for recharging, or you can buy one from a local computer store). Disconnect the HDMI cable and plug in the micro USB to your computer. Launch iTunes. You may need to disconnect power as well -- although TUAW's results on this vary. Once iTunes recognizes the unit, you can select it and click Restore. This downloads (if needed) and installs the latest firmware.