Nikon DSLR/Lens gets stuck and won't manual focus? Why? How can I fix it?

Sometimes when I switch from auto to manual focus on my camera, it won't let me take a photo. I can focus it manually, but when I press the shutter button, I hear the motor trying to focus. The camera body is acting as if it won't take a shot because nothing is in focus yet. I think the screw isn't in contact so it's not auto focusing the lens either (while on manual focus) while it thinks it should be auto focusing. The motor just keeps whining. Once in awhile, if I turn the camera off, remove the lens, and reconnect it, then I can get manual focus. It's a new Nikon DSLR from last year, using a couple lenses I had from my previous camera. Auto focus works great, no problem. I'm flying out tomorrow and won't have a chance to take it to a shop for a couple of weeks. Any suggestions?

It'd help if you'd post the exact camera name, and the names of the lenses. Also, how did you switch from AF to MF, using a switch on the camera or on the lens?

I suspect it's e.g. A D90 with older AF lenses, not AF-S ones. Correct?

Cleaning the contacts you can try. Some proper diagnostics would be a good idea which lens works? Which does not?

You may have the feature that does not allow you to take a photo if the lens is out of focus turned on.

No model number and no lens list leaves us with not enough data to answer with a coherent suggestion