Need some help diagnosing some shit bros.

I picked up a Nord Piano 3 yesterday. Apparently it was flooded at some point, owner took it apart and dried it all out then put it back together and ti sort of worked at which point he set it aside for some indeterminate time until deciding to get rid of it yesterday.
I turned it on, it sort of works. Plugged it into my computer, was recognized, nord software updated teh OS and I did a factory reset. Sent MIDI fine, except the lowest 16 keys aren't working. Also plugged headphones in and it sort of worked. Made sounds and some controls worked, but others didn't. Notably the screen seems dead, the knobs to switch instruments do nothing (but maybe I'm not doing it right since the screen is dead dunno), some of the effects section seem dead, wouldn't come on, others weren't quite functioning right, like various options that have an led when you select them, but the leds remained on.

So anyway, the question is, what exactly am I looking for when I crack it open? The keys I'm hoping it's just a bad connection at the plug or something simple, but the semi-functioning electronics.... Not sure. In previous stuff I messed with shit just worked or didn't no weird in between. Also maybe this would be better in the microcontroller general?

pic related for reference, haven't cracked it open yet.

What kind of tools do I need for testing? I've got a cheap multimeter and that's about it lol.