Join Date: Oct 2004
Location: Florence, KY
Bikes: 1954 Hetchins M.O., 1959 Viking Severn Valley, 1970 Raleigh Pro, 1972 Fuji "The Finest", 1974 Raleigh Superbe&Comp, 1976 Raleigh Team Pro, 1996 Giant Iguana, 2000 Bob Jackson Arrowhead
Try gently holding onto a section of the bare cable while you shift. If it isn't moving, the problem is almost certainly with the shift mechanism. If it does move, the problem is with something at the derailleur end.
In search of what to search for.