DISASSEMBLE CANNON A4000

What do you mean by "opened it up"? I hope you did not disassemble your lens. If you did; STOP NOW! Without training, you will never be able to reassemble your lens yourself. Contact your closest Nikon USA repair depot or a local qualified camera repair man.
If, on the other hand, you mean that you simply removed the lens from your camera and the part in question is on the rear of the lens, please post a photo of the lens with an arrow or some type of identification of the part you are talking about.
One other thing; have you asked your photography instructor to look at your lens?

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See pages 57-58 of the manual: http://gdlp01.c-wss.com/gds/6/0300007146/01/psa4000is-a3400is-a2400is-a2300-a1300-a810-cug-c-en.pdf

Try these procedures.

Most lens error codes on a Canon A4000 are caused by a broken pinion axle pin or sheared gear teeth in the lens extender gearbox. If this is your problem you can get a new gearbox or gears at: Gearbox for A4000
To watch a YouTube video on how to repair this go to: http://www.youtube.com/watch?feature=player_detailpage&v=oMpFFtzQJwg

My A4000 IS has lens error that is the lens cover could no longer cover the lens if it off

If this was indeed dropped STOP! take it to a camera shop so they can do the repairs as you could damage other parts in the camera.

What could have happend when she dropped the camera the sensor inside got stuck into position to protect it from further damage. My advice is spend a couple bucks and take it in you be glad you did!


Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/edwy_1a56970cf1ea4620

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Take a look at the suggestions at the top of page 122 of the Advanced Camera User Guide. The suggestion is that the cause may have been that the camera was still on when the memory card/battery cover was opened. Try closing the cover and then turning the camera off and then on again. Hope this helps.

Jack

This problem is caused by a stuck aperture assembly. The problem has occured on multiple models made by JVC (GR-DF430u, GR-DF450U and GR-DF470U). You have to have some degree of technical aptitude in order to disassemble the unit and access the part causing the problem. The tiny motor that opens the aperture flaps is not able to overcome the sticky oil/grease that JVC unwisely used on this part. Therefore the flaps stay closed, and the camera sees no light when you remove the lens cap. This makes the camera think you haven't removed the lens cap, causing the "lens cap" error.

If you feel like you have the skill and you are careful, you can disassemble the unit and clean the part yourself. It takes longer to take the unit apart and put back together than it does to clean the sticky oil off the part.

If you contact me, I can send you a diagram of where the part is located that you need to access. This is not recommended for amateurs, as you can damage the unit and cause other problems if you aren't somewhat skilled in disassembly of electronics.