I think you're going to have to get underneath and see if there is something damaged, bent or rusted in the linkage or the cables. The handle pulls on a short link that ends with a threaded rod for adjusting the cable tension. The two cables attach to an equalizer bar at the end of that. Put it in park or in gear, and leave the brake off, then get underneath and yank down on that rod. If you see or feel the cables moving (look where they enter the sheath), then your problem is at the handle end. If you can't get any movement in either of the cables by pulling there, then your cables are rusted. It's pretty unusual for both cables to rust solid at once if you regularly use the hand brake, but if it's an automatic and you're in the habit of using the transmission alone, it's pretty common.
Ordinarily I might recommend just pulling up on the brake as hard as you can, in hope of freeing it up. But on pre-97 XJ's, the forward anchor points for the cable sheaths are spot welded to the floor pan in a very weak way, and if the cables rusted into the sheaths, you run a risk of pulling the anchor brackets right off, or at least of causing them to flex and crack the pan, if it isn't cracked already. Even when the cables are good, the anchors flex and begin to crack, and cause poor brake holding. On my 95 I had to reinforce and bolt them to make it even passable.