If the eraser part of your pen works but the business-end doesn't, this fix may be for you. Since the only option is to replace the whole pen, it's worth the try. The interesting part: There is no "live" powered electronics in the pen (it is a simple L-C circuit for you tech-weenies out there) - truly the only way to make the pen not work is to drop it and knock it out of adjustment, use it as a crude paper punch, or get it soaked with some type of fluid such as coffee, beer or soda. The pen is an excellent design is designed to just eventually wear out. My pen is 10 years old and still looks new.
I needed a small jeweler's screwdriver for this fix (1 mm to 1.2 mm width). Carefully remove the rocker switch from the pen; it just pulls out. Don't lose it. See the image below: there is an itsy bitsy slotted screw-like device in the center (it's a tuning capacitor). For its location, follow the white arrow in the picture I've attached. Prior to turning, memorize where the slot-head points (there's a tiny triangle on it), and if possible, use a fine point sharpie to mark the screw before you adjust it. It is not a "screw" per se, but an adjustable capacitor and part of the tuned circuit.
The adjustment: Place the pen as normal on the tablet and "tweak" the capacitor by a small 1/16 or 1/8 turn in either direction until the pen reacts. If it has gotten out of "resonance" this tweak should kick it back in.