Nokia Lumia 521 - My Lumia touch screen is not responding or is responding the wrong way

1. Remove any kind of protective film or tape from the screen to check if it prevents the touch screen working. If any object is present on the top of the screen, the screen remains black.

2. Clean the screen with a soft cloth intended for that purpose.

3. Reset your phone. Press and hold the Power and Volume down keys simultaneously for 10-15 seconds. Release and the phone will restart.

4. Adjust the touch sensitivity to see if it helps, Tap Settings > touch > Touch sensitivity (note that not all phones offer this feature).