Crazy power issue? can you give me any advice!

Hey, Well I accidently dropped my iphone 4 into water :(.. The phone itself works fine if i keep using but as soon as its locked for over 1 min it wont come on unless I plug it into the wall and it will come straight on (it doesnt boot up its like it is on but not displaying anything until I plug it in)

I have tried ringing it when it is in the state of not responding and the other phone rings but the iPhone does nothing (no sound, no screen ect) However if I plug it in whilst its ringing it works instantly and i can see the call coming through and the sound starts to work..

Please please please help me or point me in the right direction.. I'd be extremely grateful for any help!