I almost gave up till I thought of the retaining clips as the problem. I just finished replacing a shattered front class and cracked digitizer, and was extremely frustrated that though the lcd still worked fine, no touch functions seemed to work. I happened to try sliding to turn of the device and that part of the screen works! that's when I remembered that one of the retaining clips had broken off during the repair. Here's what the mylar tape guy said, though it is not really clear enough for me to make sense of. I hope someone makes a video tutorial for this.
[http://www.ifixit.com/Answers/View/60226/Digitizer(Touch+screen),+Not+responding+after+Tear+down|Link text]