LCD Screen cracked down the middle

My Iphone has what I think a broken LCD screen down the middle. It does not let me unlock the phone to get into the main screen because of that crack down the middle. The outside glass is not shattered or anything. I can only answer calls using my headphone devise but not make calls. Does anyone have any suggestions or do you know whether apple can fix it for free under the warranty. I don't recall dropping it. Thanks.