You probably damaged your mother board. There is a little chip above Audio jack flex connector check if it still there if it is missing that is the reason for front camera not working.
You can create a little jumper to fix the problem. See this pic
Hope that helps.
Hallo i tried this yesterday to make a jumper between this two points and after that my front camera worked perfect but it stopped to make calls the carrier was gone and when i was trying to make a call to somebody his phone was ringing but my phone it was dead i didnt hear anything. After that i removed the bridge to see if this was the problem but the problem was still there and the front camera stopped again to work. After few hours the problem with calls stopped without to do something. Do you have hear this before? It happend beacause the jumper or is something else that just happend?
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To Johnkustic: I am having the same problem - Front camera not working after replacing the screen on iphone 4s. Is it possible for me to send the phone to you so you could do that little soldering job?
crwdns2934271:0crwdnd2934271:0 Will Schmidt crwdne2934271:0
I got the screen of my iPhone 4 changed, since then the front camera is not working. Is it an expensive job to fix?
crwdns2934271:0crwdnd2934271:0 harjinder w crwdne2934271:0
I was having the same problem. I remembered when I was having a problem with my texts not coming in, someone told me to whack it a couple of times, that worked. I decided to try it on this problem as nothing else worked, I whacked it a couple of times and wala it works. I can't believe it.
crwdns2934271:0crwdnd2934271:0 shelby crwdne2934271:0