Low wifi + no sound during call?

Hi,

A year ago I dropped my iPhone 4 (my screen got totally broken and nothing showed on but when I put it in charger the phone vibrates) so now I bought another iPhone 4 with a broken motherboard and replaced the broken motherboard with mine. The phone started normally ;I backuped my data and restored it and after that I noticed that the wifi range is very low I have to be near the router to access to wifi and when I put sim card it detects it and shows me the signal and the carrier but when I call or get a phone call I can't hear the other side ,neither can he. I tried earphones with microphones but without success I noticed that if I dial a number in the keypad (http://i.i.cbsi.com/cnwk.1d/i/tim/2011/0...) during a call the other side hears the sound of the numbers and the 3G works without any problem I'm on IOS 7.1.2.

Thanks.