My dewalt cordless drill stopped working in the middle of drilling a hole. is the trigger faulty/broken?

First before you open the tool ground yourself. The switch is probably static sensitive. Now open the tool and check for wires that may have come loose from the switch, or motor brush area. If no bad wires make sure the switch terminals are ok (not broken or bent and are tight enough to make contact with the batery terminals). Next check the brushes and make sure they move freely in the brush holders. You didn't state the model so it may not have brushes you can access. If all that is good disconnect the motor from the switch and secure the motor in a vise. Take wires with alligator clips and connect the battery directly to the motor for just a second to see if it runs. If the motor runs you have a bad switch assuming your battery is charged.