Do you have the manual
Added 45 minutes later:-
I've had a quick look at that manual, and doubt it will help you much.
It sounds like you need to try a valid Micro-SD card in there. I don't suppose you have another MX-400/450/500/550 close at hand?
I'm also wondering how the card became corrupted.
But "what's on there"? System configuration settings, I should imagine. I'm wondering if you can re-instate these (maybe using a fresh Micro-SD card) - or reset to defaults - via
one of the menu options (fingers crossed) such as Config Mode.
The Good News is that there seems to be a fair amount of spares (refurbished boards, and what-have-you) available for these monitors on line.