Get a new battery? - if it was doing the weak unlock thing for a few days, the battery could have been on its way out anyway.
Are you saying it just doesn't have any power anywhere? If so it sounds like you need to dig into/behind the dash fuse box etc. If the water corroded the positive lead there's a chance you had a dead short
iirc continuity to the large engine bay jump start post is a separate circuit
This sounds a lot like the B+ connection issue this guy had
https://www.bimmerfest.com/forums/sh...=661556&page=2