Screen protector Interference
Your screen protector may be the cause of the issue you are having. Remove your phone case and then proceed to use your touch screen. If your phone registers your finger placements, then your screen protector was the cause of your problem.
Screen is Locked
If your screen is stuck on one image and turns unresponsive, it is usually a software issue. Powering the phone on and off is a potential solution. If the phone’s display does not stay on or come on at all, then the lock button could be interfering. Try wiggling around the lock button or taking the back cover off the phone to see if there is anything interfering.
Screen Cracked
If the screen is physically cracked or damaged, then a replacement is usually the only fix here.