5s screen not working - please help

I had a problem with my speakers not working yesterday. I made an appt with the genius bar this morning and they said that the speakers may not be working because of water damage. The phone is less than a year old and I have not had any water damage, but I know that the sensors are sensitive. Anyway, they wanted to charge me $269.00 for a replacement. I decided to pass and see if I could fix the problem myself. I got home and opened the phone up to see if I could see dust or something, which there was a little. I put the phone back together and not the screen won't work. It's half grey and half light grey, split down the middle. It's responding to itunes because I was able to plug it in and back it up. Any ideas on how to fix it? Thanks