Plug it in and Flip the switch. Lol
Assuming it powers up-- and the master password wasn't set:
You should get a "B>" prompt
Input "bld" and see if anything happens.
If you get any response beyond a blank screen you can ebay the parts. If not the memory is shot, or missing, among any other issues; and you'll make more from scrap than selling it fixed. Rare and dead doesn't make it expensive. Unfortunately. Bills to fix these start at 5 digits. Not counting labour. But you'll get some fair value still, pulling it all apart.
There's a real good
breakdown here with inside shots.
I've sent quite a few various parts from the 36 series to boardsort and most have fallen into peripheral but with some in midgrade and about a third being telco. The transformer will fetch a nice bit at a local yard too. And silver and tin when clean always have buyers. Plus all that steel and well...!
That link though should wet your appetite!
Still can't figure out what made the 2xxx self processing terminals $10,000, and the XT just $3000 when they were generally identical; but that's a whole nother discussion
As long as it was off, water would have little impact. Biggest issue I've seen was mice. Attracted to the em fields. Like cars they make a bit of an issue chewing through things.