My camera turns off when the lense is attached. Once I take it off its fine.

Either you have an older, nonelectrical lens, or the lens is faulty. Without knowing the make and model of the camera and the lens, it's not possible for me to tell you which case is appropriate.

Apparently the lens is faulty. Or it may have dirty contacts.

Take the lens to a camera store and try it on one of their cameras. If you get the same error, the lens probably is faulty.

Try another lens,or set the camera to shoot without lens.This could help you narrow down if it's the lens or the camera.

If the camera works fine in fully automatic mode, but onot in AV or P, it is likely your settings. Trying increasing your ISO (larger number) and increasing your aperture (smaller number). If you don't have sufficient light or a fast enough lens, the shutter be force to operate more slowly. If the camera also has issue in automatic mode, then I would try the following:

Turn off the camera and remove the lens (in a clean, dust-free environment) and lightly clean the contacts on the lens and camera body with isopropyl alcohol. Once your sure the contacts and surrounding surfaces are clean and dry, re-attach the lens. Power on and try...

Good day,

This is a common problem and sometimes can be fixed.
Please see details on my tip on how to fix this error here:

http://www.fixya.com/support/r7041378-digital_camera_lens_problems

Let me know if my tip was useful for your problem!

Regards

clean brass contacts with qtip and rubbing alcohol. let air dry couple of hours. do the body and the lens. hope that helps

Unfortunately, there are electrical differences between early and later Sigma lenses. Although the bayonet connection is the same, and the lens can fit, it will not necessarily connect electrically with the connections on the camera. Sigma can modify the lens for you, but this can be quite costly, and you may be cheaper to look for an alternative lens.

i had a similar problem...my lense woudnt go back in either, but it kept saying low battery and bleeping. I realised that my lense was stuck skwint, and that was what was causing the problem, once i straigtend up my lense it folded bak into the camera and worked fine wen i turned my camera on :D

Make sure the aperture ring is set to the minimum f-stop number, ie f22,f32. It is usually colour coded orange

i have exactly the same problem with exactly the same camera. It happened to me once before but by 'fiddling' with it, it seemed to catch back in place and turn on again. but this time it wont work. seems like a design fauly from samsung?