How about following mode?
Can you enter the each mode?
Push with power switch +each key and hold 2-3 second.
Menu Mode:
Push Power switch with ALL+1+A-B.
MIDI date record mode:
Push power sw with Vol+Tempo+Trance
MIDI excrusive mode:
Push power sw with Metro+MIDI
Open the lower panel.
And check I/O sheet LED.
(see the attached file)
I guess CPU sheet is dead.
It is common symptom in MX series.
I recommend to call Yamaha France.
