Wow, such a simple question, such a wrong turn at Albuquerque...
Which Hornady hand primer do you have? Does the end of your handle move towards the top of the primer, or towards the bottom?
I would tend to assume that you have the large primer seater stuck in a small primer tray, but that may not be the case, since your post sort of implies that it did work at some point.
With the handle that moves towards the top, you should be able to remove the link follower and use a wooden dowel or brass rod to drive the primer seater out of the tray.
With the handle that moves towards the bottom, it should work the same, but it's a little more difficult to disassemble in that way.
Next time you get it disassembled, drop the primer seating pistons into the housing and let them travel the full ROM without handles or springs assembled. Feel your way around whether it has a burr or an oversized diameter that might be causing your hang up.