Now that I've had some time to think about it, I want to say that when I encountered the CHECKSUM message it gave you a Y/N option. If this is the case with your controller, you should be able to get your screen back by pressing "Y". The system should thereafter be fully operational, and should...
The battery (soldered to the circuit board that is directly behind the keyboard (or pad)) has most likely expired. Expose that board and note the part number of the small cylindrical battery (which should be either blue or green). It is most likely a VARTA 2/30 DK 2.4V. A replacement can be...
