HOW TO GET NIKON D90 KIT LENS TO AUTOFOCUS?

I changed it to a 50mm lens and it was fine

then when i changed it back to my kit lens it won't autofocus.

eg. When i half press it, there's no beep and it doesn't focus itself.

how do i solve this?

THE AUTOFOCUS SWITCH ON THE LENS & CAMERA IS ON A ALREADY

Added (1). The lens is locked in properly.
everyime i half press the shutter release button it says "r13" not sure whether that's related thou.

what should i set my metering/bracketing etc to be so it will auto focus!

Added (2). Yes i have removed the lens and put it back in. I reset all custom settings.still no autofocus

Have you tried to remove the lens and re-attach it again?

If so, with the power off the camera, clean the contacts with a dry microfiber cloth - both the lens and camera body. Make sure you don't get any dust in the sensor.

http://www.althephoto.com

Yes but have you tried cleaning the contacts? Do that first and re-lock the lens. If none of this helps call Nikon for help.

Which kit lens (Model) is this? Does it have a [M/A - M] switch or a [M - A] switch on the side of the lens? If so, make sure that the switch on the lens is set to M/A or A, so the auto focus is engaged.

Also make sure the lens is fully locked into place and engaged.

Are you saying it WILL NOT lock onto a focus? Meaning at half pressing the shutter release the lens does try to focus but never gets it locked in?

Or is it:

You press the shutter release half way and the lens does nothing, nothing at all?

If you switch every thing to MANUAL (camera body and lens) then manually focus on the subject is the image sharp or close to sharp?

And what kit lens do you have?