I'm afraid water has entered your phone. However you could try to dry it off at a fan(not from a heated source) and see if it vibrates when you turn press the ON button.
If there's not vibration,means your phone is totally dead. If there is a vibration,means that the display is crooked somewhere.
*sometimes the flaps aren't reliable enough
In such cases,you should bring the phone to your local Xperia Service Center to get it fixed. It might costs you money but it depends.
Plus,did you ever dived into a pool with your phone or submerged your phone in liquids beside fresh water?
