No signal- searching, no flashlight, front camera freezing

Hi, i have bought second hand iPhone 4 with:

• bad signal reception - phone is still searching or displays no service (sim card is recognized).

• flashlight is not working
• front camera app freeze when i try to run it
• vibrations arent working

I have tried:

replace antena - still no signal

replace rear camera with flash - still not working

replace vibration motor - still not working

I have noticed little damaged battery connector

Is there some thing which can cause all these problems ?

Thanx!