I have a new Nikon 3100. The problem now is my 18-55 zoom lens is locked and it won't move. In the manual setting and by unclicking the outer lens auto button, the focus front lens is fine. It'

Not if your other lenses work ok. I would contact the Nikon Repair Depot that cleaned it.

You're on the right track with oxidation. Try cleaning the contacts in the body and on the lens with contact cleaner, and let it dry. Remove the battery, and clean the contacts inside the camera.

Try taking the lens off and remounting it.

Just a thought - are your Image Stabilizer and Auto Focus switches On or Off?
Might be worth experimenting with them.
Otherwise, sorry, can't help.
May be necessary to contact your vendor.

if other auto-focus lenses work, then it is likely that this particular lens has a defect I suggest you send it in to Nikon for servicing

Could be your lens is not communication with the body. If the lens is not telling the camera that the AF has locked on an object then it won't allow the camera to fire. Make sure that the camera is indeed locking the AF on the object. If there isn't enough contrast (for example a plain wall) then it wont be able to lock onto it. This would usually explain why it works on manual but not on auto (I assume you mean the focus setting and not the camera's modes). If you're still having issues I recommend you contact a nearby Nikon authorized service center for assistance and possible repairs. Hope this helps!

Hiram
Photo Tech Repair Service
110 East 13th Street
New York, NY 10003
212-673-8400

You must lock the aperture ring to f/22, so the camera can engage the aperture adjustment lever on the lens. Then, you can change the aperture with the command wheel.

When you change the aperture with the command wheel the aperture ring on the lens doesn't move when the camera actually adjusts the lens aperture.

Take the lens off and locate the aperture adjustment lever on the lens mount.

Unfortunately, this won't work with older AF lenses. So if you are using an older lens, the only thing you can do is change the camera setting to M (Manual) to adjust the aperture on the lens yourself.

Most digital cameras jams are the cost of lens problems while zooming, with Nikon Coolpix S4000, simply use your fingers carefully pulling on the lens while turning the camera on. this can be done by getting your fingernail under the lens opening and gently pull.

Have a close look at the iris ring to see if any think is broking off
or try moving the lens when it is locked on the camera to see if you lose the fee if so it may need a new mount

You might like to check if the A/M slider switch on the lens by the Nikon label is set to A.
It sometimes gets moved accidently.
Set to M the lens will not autofocus.