The first thing you should check are the tracking eyes. If it's not a dual eye tracking system, which I'm guessing it isn't, then one of the tracking eyes/black box will be the receiver and the other eye/black box is the emitter. If you still have the manual for this machine, sometimes AEM, which has been bought out by Timesavers, will put a small business card sized laminated piece of paper that has a square located in the center of it.This is used to see if the emitter is reflecting the beam to the receiver. Radio Shak may still sell the infrared detection cards as well. Once placed in front of the emitter, you should see the square box glow. If that is the case, then go to your air cylinder and pull the air supply line off it. Place your hand in front of the tracking eyes and you should feel a puff of air coming through the line. If not, then trace the air line back to the air solenoid valve (usually a blue Mac valve). Once located, do the same procedure of placing your hand in front of the eyes and listen/feel for a "clicking noise". If there is no "clicking noise", then either your valve has gone bad, or your tracking eye receiver has gone bad in which case I would recommend replacing both the emitter and receiver. One other thing to check is the exhaust port on the solenoid valve. Most times there will be an exhaust muffler screwed into it. If you have bad air, this muffler tends to clog up and will reduce the air being released, in which case you tracking cylinder will be slow to react, or not react at all. Also check the tracking cylinder piston. Spray Windex on the piston where it enters the body of the cylinder and see if you notice "bubbles coming from it. If you do, most likely you seal is worn and you will need to replace the cylinder or in some case rebuild it.