If it was flood-water, chances are that the water wasn't clean. That means trouble.

I would suggest pulling the whole thing apart. Pull out the socketed chips too, just record which sockets they came from. Give the mainboard, case, trays, and bracket a good shower. Let the mainboard and case dry. Maybe you'll give it a week to dry out, or maybe you'll use a hair dryer. Just make sure it is completely dry. You may want to pull the power supply apart too, and do the same. In the case of the PSU enclosure and the metal trays/brackets, it's probably best to dry them off with a towel.

Once everything is good and dry, reassemble it without adding the floppy drive or hard drice. It may work. If it does work, you'll probably still need a new ard dive and floppy drive. If it doesn't work, its probably a power supply issue.