I know this topic has been discussed before, but I cannot find the thread anywhere. I have a PRO 39 that works, but the keypad does nothing. No matter which way I put the keylock, none of the buttons work. It just scans forever and won't accept any functions. I took it apart, and tried to clean the circuit board with light sandpaper. Can someone else give me some ideas here, I would hate to sell this scanner as parts.