I had a -M also.
When I took apart the refurb Pronto with the $1.99 Sears Torx T6 tool, I noticed 1 of 3 screws were holding the LCD, and 2 of 4 were holding the circuit board. I put all three on the LCD,and now it works. Best $1.99 I ever spent. Need to find three more screws for the circuit board though.