If it ain't the neutral safety the most common problem is the battery posts and clamps are dirty. You'll still get enough power through for lights and guages but not enough amperage to even click the starter. Also if you're using the battery post connectors that also have a clamp to squeeze the positive cable check to make sure that the end olf the cable doesn't have the same oxide crud build up preventing full amps to the starter. :evil2:
Hope this helps