There could be a few reasons why your DS4 controller isn't working. Firstly, make sure that it's plugged into the correct port on your computer - the one that's labelled "DS4" or "Controller." If you're using a USB cable, make sure that it's fully plugged in and not just have one end sticking out. If you're still having trouble, try resetting your controller by holding down the power button for 10 seconds, then releasing it.