Had the same issue.. my display was a bit loose, so i decided to reglue it, after that process was done, touchscreen stopped working. After a bit of trying i figured out that it in my case it was the speaker! It somehow pushes from the backside. Didnt find out why though.
I removed it now it works all exept that i have no music anymore (phonecalls still work)
Maybe to someone it could be useful
Removing the speaker is very easily done. Removing the backcover takes a bit of time.