Trying to fix iphone 4 but not sure what is wrong

[netrate]

I was given an Iphone 4 from a friend at work to see what I could do.
She told me that it was dropped in water and she dried it out in rice.

Here are the symptoms:
1) It does not turn on
2) when I plug it into the charger, sometimes I will get two successive vibrationsindicating there might still be life in it.
3) the vibrations also occur occasionally after I take it off the charger and I am fiddling around with the phone
4) No lights at all
5) Tried booting to safe mode (hold the home and top bottom) nothing happens.

Now, I have taken out the screws and have the battery pack removed from the back, so I am able to disassemble this if needs be. How should I approach the rest of the repair?

 

[netrate]

Forgot to add, I haven't taken out the battery or any of the components yet and I have not put anything in Rice - the original owner said she did that.

 

[PMehta]

Forgot to add, I haven't taken out the battery or any of the components yet and I have not put anything in Rice - the original owner said she did that.

If it vibrates when you plug it in, that might just be a screen issue. If you have any spares lying around I would try and replace it and see if that fixes it.

It could also be that while the battery is charging when you plug it in [gives you the vibrating notification] the battery itself is dead and it's charging properly or holding enough charge to allow the phone to turn on. Replacing both the battery and the screen might solve the issue.