iPhone 5s screen blank after dropping in water

Hi,

So i recently got a dead iPhone 5s from a friend, because he knew i liked that kinda stuff. He dropped it in the toilet and it stopped working. He left it 3 days in rice but still no effect.

Now it kinda turns on, if i plug a charger in, it will flash the apple logo and then the screen goes blank, but stays on (i can see the backlight still being on). It will stay like that untill i unplug the charger, then it turns off. It will sometimes display the dead battery icon if i plug it in, but thats on rare occasions. (Also if i hold the power button and home button at the same time the Apple logo will stay on longer, but still not long enough to boot)

I tried connecting the phone to iTunes, and it actually recognised it and told me the software was bad and needed to be restored. I tried that, but when the phone had to reboot it just shutted off and didnt turn back on again, so that wasn't a succes either.

I went to a repair shop to get all the water cleaned out and getting the phone tested. After an hour they told me they also didnt know whats wrong. I've also called Apple, and they didnt say too much, just the price of a refurbished iPhone 5s etc.

Does anyone know what the problem is with this phone? Thanks!