built in microphone not working after falling

Hello,

I dropped my macbook pro (twice) a while ago and now it doesn't pick up sound anymore, I don't think it's broken because a while ago I was talking on skype and the sound was falling away and coming back and after pressing on th top of the case the sound returned but now no one can hear me, only by tapping the left speaker will give me some noise detection in sound/system prefs so I believe it's a bad connection but cannot find the tutorial on the microphone.

And I bought a a bottom case to replace the damaged one but I kinda don't have the guts to replace it !