Hi,
Have you tried to reset the keyboard to its' factory default condition to see if this resolves the problem for you.
Starting with the power off:
While holding the rightmost white key on the keyboard (C7) along with the three rightmost black keys (F#6, G#6, and A#6), turn the power switch on. "Clr" will appear on the display.
NOTE: Do not turn off the power while Clr is showing on the display.