If the device is under warranty, I would contact the manufacturer about a fix. You don't want to mess with it and void the warranty.
If it isn't, you are going to probably have to open up the device to see if it is just stuck, or if the interior button is damaged or broken and needing replacing. If you are comfortable doing the work yourself, try that. You may even find videos online to walk you through opening it up. If you don't feel comfortable doing the work yourself, then try contacting a local tech.