James is correct. I do not have a manual on this machine but there are 2 possibilities.
This head is very similar to the R2E3 and R2E4 in that it has all the fiberglass around it.
The R sesies had a chain and sprocket arraingment to the actual shaft that noved the bull gear up and down. On one of the sprockets is a screw that is seen on a switch to indicate if it is in high or low gear.
Newer machines (V2XT) and possibly the X-26 have a prox switch built into the block that sees the plunger attached to the lever that locks it in gear. there may be dirt there.
Also it could be a broken wire, switch out of adjustment etc. How was the machine moved? It may shed light on where to start looking.
George
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)