Hi Bob
Have you tried to reset to factory settings? You are going to lose all your data after reset.
If this doesn't help then it is the actual digitizer. I have one of them before and there was nothing visible to be wrong but when i open it i saw the cable for the digitizer was somehow ripped off. I have no idea why probably too much heat near the cable or something else i don't know. But after I replace the digitizer all works great. Now my dad is using it so happy days.
Hope this help