I am a V70 guy, but I will assume that the S80 door is the same as the V70 door.

This link will take you to a detailed and illustrated procedure for replacing the lock mechanism. Just ignore all that stuff about disassembling the lock in order to repair the Red Evil Plastic Lever.

http://www.volvospeed.com/Repair/v70latch1.php

And, here is the standard mantra for all who embark on lock replacement: You will swear that it is impossible to remove the disconnected lock from the door. However, many of us have done it. Your patience and perserverance will be rewarded.

The typical cause of this failure is trying to lock or unlock a door electrically, while someone is pulling on the exterior handle. That is almost guaranteed to break the aforementioned REPL. Even if this was not the cause of your current failure, do not let it be the cause of a future failure. You will not want to endure another lock replacement.

Mort,
It is going to be hard to take the panel off with the door closed. When you unlock the car, does the little black knob pop up? Can you open the door from the outside?

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.

Did you accidentally press the child safety button at the panel on the driver's armrest? That might only affect the window, but I think there's also a special safety latch in the door jam. Not sure if these would cause this but maybe worth checking the owners manual to see how they work.