Nikon D5100 Troubles?

I accidentally dropped my lens and for about a week whenever I tried to attach the lens, I would get a message on the camera that said "No lens attached". After messing around with the lens, I found the problem and I can now use the camera. The problem is it isn't adjusting to exposure or auto focusing anymore. I only dropped the lens not the whole camera. Any ideas for how to fix it? I let a friend mess with the camera some too and I don't know what settings they changed. Do I need to get a new lens or send it back to Nikon? Please help. Thanks.

Added (1). I've only had the camera and lens for about 3 or 4 months. This is the first time that it's ever been dropped. I don't have a warranty on it because a relative had gotten it for me and they didn't get the warranty. I do still have all of the papers in the original box, people have told me that they thought there was a limited warranty somewhere in there that you could sign up for online?

Your friend has probably messed with the settings. In the menu there will be the option to restore settings to factory default. Find it and re-set it.

Has the autofocus on the lens ever worked after dropping it?

Make sure it is not something as simple as the lens switch in the M (manual focus) position.

If the lens is bad, it's probably not worth returning to Nikon. The 5yr warranty usually does not cover damage (that is why it is limited), so Nikon will probably not repair it under warranty.

But you can buy a replacement lens for around $100, so the cost of a new lens is probably less than what repairs would cost.

A warranty only covers manufacturer defects, not owner neglect. Sell the lens as " not working / as is", and buy a new one.