take the battery out of the phone, put it back in. it may refresh the phone & it will start working correctly.
depending on how old the phone is, you could always upgrade & get a new one if that doesn't work, or if it IS fairly new they can send your phone in to their service department & replace the phone!
the other thing is, your phone may have water damage, & there is no fix for that. You wuold have to buy a used phone or a new one! OR if you have insurnace, you can get a new one for a low deductible =) GOOD LUCK EITHER WAY! ;-)