That actually just occurred to my 800 about a month ago.
The up/down/side to side keys went out,then the menu key also.
I disassembled to see if there was a visible issue,to my surprise
the ribbon connecting the keypad to the board was angled. No drop,
it was a desk scanner,,I pushed in the ribbon,added a piece of
masking/blue painters tape to secure it and it worked fine.