1998 Chevy Astro rear door

Do you have power locks and if so do the other doors unlock with the automatic lock button? If not try changing the power lock fuse under the dash,(the same fuse could operate other things too so check them all if your not sure wich one it is.) That might be the problem. My 98 astro rear hatch door did the same thing, and (if you have power locks the key wont open it no matter what if the fuse is blown.) I dont know why they designed them that way seems kinda strange to me. If you have manual locks try crawling in back and removing the panel just around the window. If you get it off theres a long thin rod just below the bottom of the window try pulling it to one side or the other and the door should open. If the fuse is not blowqn and the rest of the doors open with the power lock button you might have to try openning it by removing the panal as i described before. I hope it helps. Good Luck!!