Have either of them ever worked on your current set-ups? I ask because the limit screws may be adjusted for another dropout and they may be preventing the shifter from moving the parallelogram sufficiently in order to move the chain to your larger rear cogs.

If they have worked previously (and in any case), check:

- the cable hasn't stretched
- the cable hasn't slipped in the pinch bolt on the derailleur
- hanger alignment
- that cables are sufficiently lubed / no gunk in the housing.

HTH