autoexposure error message in window

Sadly, It sounds like the lens or the lens mount got damaged so the electrical signals to the iris controls is not functioning. If you can try a second lens does it fail with it as well? If so your issue is within the body if it works then you may want to think about a new lens Vs repairing as the cost of fixing maybe close to the replacement price.

I had a smilar experience 2 years ago. The best option is to setthe dail to Manual (M) it should work

"If the camera was dropped do the following which only requires a moderate skill level.

Remove the battery and SD cardRemove all small screws from the bottom housing cover including the hidden one within the battery compartment.Remove the bottom plastic cover. Underneath is a metal support bracket. Carefully inspect the corners of this bracket. Any impact can bend this bracket which will pinch the FPC ribbon cable which connects to the rear LCD. The damaged FPC cable will give you the “auto exposure error"".This cable can be purchased online for as little as $6."

"I had the auto exposure issue on my D5100, following the in depth tear down https://fr.ifixit.com/Tutoriel/Nikon+D51...

to detach the back cover (with the lcd), I could indeed find that it was just one of the zero force insertion ribbon that had its lid opened thus the contact was wrong. Closing the small lid did the trick - that’s what the guy in the uTube video was also saying, and it’s true - however I would not recommend using the video but rather the cristal cleat iFixit manual."