Have you ever changed the internal Lithium Battery. Try the reset here, although it is for a different model. The Keyboard was actually made by Casio and sold with the Radio Shack name on it.
REPLACING THE MEMORY BATTERY
Your keyboard uses one lithium battery to protect some types of data when it is turned off. This battery is installed at the factory,
and lasts up to 5 years. If the keyboard's memory is erased when you turn the keyboard off, take the keyboard to your local Radio Shack store to replace the lithium battery.
RESETTING THE KEYBOARD
Note: Resetting the keyboard clears all information you stored in the keyboard's memory, including the parameter settings, song
sequencer, pattern sequencer, and registration memory. Resetting the keyboard's parameter settings clears only those settings from
the keyboard's memory. To reset the keyboard, turn the power off.
Then hold down ENTER. Reset? appears. Press YES.
https://www.google.com/search?q=Radio+Shack+Midi+Keyboard+MD-4072+reset
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