As far as adjusting the pen sensitivity , the first thing that you should do is open up the wacom settings, then take your pen and press hard, if the little blue bar fills up then the problem probably exists in photoshop.
Marc goes over how to get to the wacom settings in the photoshop for digital production lessons, if the pressure bar isn't filling up you can mess with the settings there a bit and see if you can get it to do so. If it still wont, there is a chance that your pen is damaged, but try doing the calibration first.