Have you contacted the manufacturer or supplier? Is the unit still under warranty? Obviously there are internal problems in the resistance unit but most of these are unservicable so it's probably going to have to be replaced either by the maker or with your own dime.

BTW, I have a Performance Travel Trac (their house-brand made by Elite) that is four or five years old and still working perfectly. AFAIK, Performance will warranty their products pretty much indefinitely.