@Dawn83: What is the model number and current Android version of your phone (this information can be found in Settings > About Phone)? In the meantime can you try pressing the Volume Down and Side Keys together for around 10 seconds until the device restarts, as this will perform a Soft Reset and address any temporary software issues.
@Dawn83: Are you pressing and holding the Side Key to access your power options? If so, and if it's not responding, then please swipe from the top of the screen to the bottom, then again to enlarge the Quick Panel, and tap the power symbol in the top right corner to access the options from here. While you're here, tap Side Key Settings > Press and Hold > Power Off Menu to ensure that the Side Key is mapped to the right function.
