Why is my screen not responding to touch?

Could be a software problem or it could be a hardware problem.

If it's software then restarting the phone and/or booting into safe mode should get it working again. If it does work in safe mode but not on a regular boot, then you've got an app interfering with the touch screen and you'll need to go through and delete them until you find the offending one. If your phone requires you to tap a button on the screen to restart it (like mine does), you can plug a wired mouse into your USB port and use that to mouse to the button and click on it.

If no software solutions work, then chances are your digitizer has failed. On all modern phones the touch screen is bonded to the display so the entire display has to be replaced in order to fix it. iFixit doesn't have a guide, but I located one on a French site that has exactly what you need.

Galaxy A04s Screen Block Repair - Free Guide - SOSav.fr