Sounds like a faulty digitizer. Is it responding to your touch at all? If not, you can check the connections, maybe clean them with some isopropyl alcohol on a cotton swab.
If it still doesn't work after that, you'll probably have to replace the digitizer. You can choose between this: [product|IF126-001-2] which would require you to switch out the home button and front camera, or you can buy this: [product|IF126-000-3] with the home button and front camera included.