Mark is spot on with his advice.  If you have not been giving each zerk on the unloader at least 7 pumps of grease every day, it will seize and not move.  It happened to my 1680 before I started "wasting" grease on the turret.  I did have times I could get someone to push on the unloading auger while I held the switch open, just to get it started.  Once seized, just greasing will not solve the problem, you need to move the auger full out and grease until you think you did enought, then grease some more, move the auger half way and do the same, and move it all the way back and continue to add grease.  It should be slick enough so you can bump the auger out of the cradle and it will move a little.  That little cylinder that moves it is not very big, and doesn't have much pressure.

Another thing that caused the auger not to go out is if there is pressure somewhere else on the hydraulic system.  For example, if the mud hog is on and straining a little, the unloading auger won't go out, as fluid is going elsewhere, and the unloading auger is the last thing to get oil.  If the wheel cylinders are under pressure trying to turn the rear wheels, the auger won't retract either.

I'll bet the problem is lack of grease.  I believe I remember 7 zerks on that panel on the auger that take grease to various parts of the turning circle.  Be kind to them, feed them well, and they will treat you much better.

(Added later)  When I got my electric Lincoln gun, I had much less trouble, as I over greased more often since it did not take as much effort.  7 pumps per zerk is a minimum, you can't hardly get enough grease on that circle.