I had the same problem of not being able to reopen a paperwhite. Tried all the usual methods to no avail so plugged it into my PC. It showed up in Explorer with all its contents which I download to my PC as a backup. Unplugged the Kindle and restarted it. The Kindle response was slow so I did a full power down by holding in the power button for a few seconds and now it is functioning correctly. (Fingers crossed)