Hi, my S80 only gives a single click when the key is turned in the ignition. All electronics in the car work fine, including gauges and seats. I was in a wreck with minor damage to a quarter panel and there doesn't seem to be anything wrong with the engine. A lot of people had said the starter, but I wanted to check before I threw away 150$

 

It could be the starter...

Try this old technique.

Put the car in drive (I realize the car will not start, but you should be able to put the car in drive with the ignition on and foot on the brake). Have someone push the car forward, again I realize the car will not want to move as it is in gear but your not trying to push start it, you're just trying to turn the starter motor a little. Put the car back in park and then try to start the car again. It may be just enough to turn the starter motor. I used to do this to my Nissan Altima sometimes.

 

Actually, there is a piece on the starter. Solenoid, I guess? That happens to be broken off. Here are some pictures.

 

Yeah, that would cause a problem now wouldn't it.