I have paperwhite 8th gen. The screen has been frozen for over 24 hours. I can't switch it off or access the main menu so how do I reboot it
Welcome to the Forums!
Have you already tried the following:
Press and hold, or slide and hold, the Power button for a full 40 seconds, even after the screen goes blank, then let go. Press or slide the power button to restart if the device does not start up again on its own.
Let me know if this resolves your issue.