I can't get into my iPhone 4s from the home screen. It seems the screen won't sense any touch?

I try to open the iPhone from the homescreen, but it doesn't seem to sense the touch to open it. If I get a call, I can touch to answer it, or I can use voice commands to open a feature, but once it is open, it doesn't seem to sense my touch to do anything in the app. If it opens and I close the app, then its at the app screen, but I can't touch any of the other apps to open anything else. It just suddenly started this a little while ago. It was working fine about an hour before this started, and I haven't dropped it or done anything with it otherwise. Can anyone help?
Oh, and I only just got this phone 2 weeks ago, used… But it was working just fine all along until just now.
Added (1). Also, I can't even turn it off to see if turning it off and then back on again will help. So FRUSTRATING!

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