It could be too late now but it would have been best to dry it before plugging it in. This is easily enough done by just leaving it in sunlight for a few hours. If there was moisture inside when plugged in, it can begin to corrode and damage stuff. You might still try sunlight for a while and give it a try the next day. If it fails to work then, consider it a goner.
So I dropped my USB drive outside my front door (fell off my keyring), where it lay overnight with light rain. At first, it still worked ok, but it became less reliable, and now computers can't read it. I took off the plastic covering and it all looks connected inside and perfectly dry.
Any ideas on how to fix it anyone?