I suppose you could check to see if the cable to the lcd module came loose or something.
If the microcontroller wasn't working the device would probably not work, at the very least the leds/fans/lcd backlight/buttons would not work properly. If all of those work as expected you can be fairly sure it's just an lcd problem.
I've created a library for interfacing with the microcontroller on these devices, though it needs to be running linux (not the stock firmware) to work.
https://github.com/1000001101000/Python_buffalo_libmiconI've been working on getting this model running linux but haven't had much success so far, I can get it to boot and recognize most of the hardware but haven't got sata working (kind of important on a nas). I have been able to confirm that the microcontroller library works on this model.
If I ever get the whole thing working that would give you some more tools to troubleshoot with but ultimately if the LCD isn't displaying messages and removing power from the microcontroller doesn't work it pretty much has to be an iccue with the lcd or it's connection to the board.