My very tall very old friend yanked and tugged at the wrong end of the belt and it became stuck in the fully retracted position with only about 1/4 inch of play in the belt.
Here is what I did to fix it.
Remove the interior panel-it just clicks in under the rubber door seal so it will pop right out. With that pulled out of the way (I left the top fastener attached) you'll see a black plastic cover over the belt reel. That pops off as well and you'll see 3 yellow plastic wheels with teeth. At the top there is a white plastic lever. Push that lever to disengage the lock and tug the belt. After several tries I got the belt to retract, so now it works as usual. Button it all together, snap the panel back and go drive.
Good luck.
Tom