APPLE TV COULD NOT BE RESTORED

When I switched on my 3rd Gen Apple TV on 2 days ago it said there was an update. But when I tried to update it, the update failed. It then told me to restore the device by connecting to itunes. When I connect it to itunes it is unable to restore the device - "Apple TV could not be restored. An unknown error occured(9)". I've tried different micro USB cables and even different machines (imac and work PC) but same error message every time. Any ideas on how to fix this, or is an inconvenient trip to the apple store required. The device is only 3 months old so will be covered under warranty, just annoyed it has broken so quickly!