Do you have free wheeling hubs in the front that are unlocked?
I'd put it securely on 4 jack stands and observe what the propshafts are doing, if anything, when the red lever is fully forward and fully back.
My bet however is on rust in something if it's been sitting for a year, assuming it really did work when you bought it.
I have seen the dust cover dented when driving in 2WD and so it then won't go in to 4WD.
Tom Rowe
Four wheel drive allows you to get stuck
in places even more inaccessible.
62 88 reg
67 NADA x2
74 Air Portable - The Antichrist (tag 6A666)
95 D1 - R380
95 D90 - R380
97 D1 - ZF