Does the machine have a neutral lock lever as many Cats have?
That is a good possibility the parking brake moves but the interlock could be frozen this thing has been sitting since 2001
When you start it up you will have to put it in gear every time too first or second. I would try and get some air in to it I bet things will start to happen after that. Your far left petal is a clutch but air operated too.
There is no conventional clutch on this machine, the left pedal brakes and dumps oil from the selected powershift clutch to break drive, I reckon you will find part of the interlock linkage frozen up as already discussed.