I can’t say that I had a similar problem, but in general - when I received a parcel of used EX8000 - it also did not start due to a faulty OS. I had to restart the OS via SysEx transfer. And after that - the synthesizer entered the working mode.
you can try to restart it this way “factory reset”
PS: Click can switch DW mode - in tape recording mode! are you control it? can you see “TAPE” at 7-seg.display? or standard info view? likesee below pic.
