pull half shafts out (if thier not broken) and then engage 4 wd diff lock and pull forward if anythings broken it will drop into the diff and the diff will lock. happened to me with my defender lost 4wd unless in diff lock pulled the half shafts out and were fine pulled foward and someting dropped into the diff ,diff locked up and then popped out the back. more cautious route may start with draining diff oil look for metal bits, or castle nut come loose at front of diff