First thing is to remove the wheel and move the arm. If there is tension great. If its limper than a noodle replace the RD.

If there is tension or you are skipping step one. Reset everything to zero. Tighten the H and L screws and the B screw all the way down. Do the same with the barrel adjuster. Zero the rear D in using by slowing backing things out until you have it right.

Did it take a hit, was the box damaged? I find it hard to believe that the rear D took a hard enough whack that the spring lost its focus. I have taken some hard falls on the rear d and had to readjust my hanger, but the D was fine. Running a 105 long cage from probably the same year with plenty of miles on it.

Try to zero it out then readjust.