Mine is ten years old and start quitting on me during runs.  Talk about ruining a good run!  It would start working after a few minutes but still very frustrating.  I ordered a new circuit breaker/reset switch, which is the same button I was pushing to reset the treadmill after it stopped.  I ordered the part online from the Treadmill doctor at http://www.proformtreadmillparts.com/. The part was like $15 plus shipping.  Easy to install, just removed a few screws underneath the treadmill slide off the 2 wires, snap out the old part and install the new circuit breaker.   It’s been 3 weeks and about 12 runs and the problem seams to be corrected.  I was thrilled; I was ready to buy a new treadmill.  Now I can save my cash, cha-ching.  Good Luck.
                 Patrick
                
 January 2007