Did you touch the "reset" selection? (If yes, you are screwed).
Install this (it does not matter if it has already been installed):
https://www.mobileread.com/forums/sh...68&postcount=4
It is a special package that you put in the visible, USB storage, top level, then you can use Amazon's UYK menu entry (or just reboot into it) to do the install, it should repair whatever is wrong with ;log mrpi