Probably the infamous aperture gear breaking. In this case it will need to be repaired. You can confirm this if when you press the shutter you will hear a "werrring" sound of a motor spinning freely. What's happened is a black pinion gear has split and isn't connecting with the motor shaft properly. You find this gear on ebay if you search "D80 parts". It's quite an in depth repair and would require a bit of bravery, complete dissasembly of the body and soldering knowledge but I have found a few youtube tutorials on the subject.
https://youtube.com/playlist?list=PLZqxTp6qH4AO4LU7q8HQ4xvgUPxhur22b&si=Zy3z4zrE9ahIHoZ4