You need a better drill. Get one that has an option for either high speed or high torque. Use the high torque for screws. Also, you should be able to adjust how much power it exerts. Make sure the bit fits the screw perfectly. If it's off, it will strip the screw unless you press down extremely hard, and even then the screw might strip. Lastly, pre-drill the holes with a bit slightly smaller than the screw.