DIAGNOSIS The touch digitizer has likely frozen or the software has a glitch holding the touch layer hostage. It's a common hiccup with wall-mounted touchscreens.
FIX Do a hard restart. Press and hold the mic off button and the volume down button for about 20 seconds. Keep holding even after the screen goes black. Release when you see the Amazon logo reappear. This performs a full power cycle, which clears the touch controller's memory. Give it a minute to fully boot up, then try the screen.
IF THAT DIDN'T WORK Check for a screen protector or if the screen is extremely dirty. A poorly applied aftermarket screen protector or a thick film of grease can confuse the capacitive touch. Give it a clean with a dry, soft microfiber cloth. Also, make sure the device isn't overheating from direct sun or being mounted right over a heat vent.
HEADS UP If the screen is physically cracked, even slightly, it can disrupt the touch layer. Amazon won't repair these; you'd be looking at a full unit replacement. Handle it like a big tablet when mounting or adjusting.