Several reasons the lens may not adjust:
-the camera may have gone to sleep, and you need to wake it up first
-there may be no adjustment needed
-in low contrast situations the camera may not be able to get a lock
You do not say but I assume you mean that when you take a shot and get no red light it is out of focus?
The owners manual is not complicated, if anything it is too simplistic. It is written to describe the functions of the camera, not how to use them. I think a lot of us would appreciate something that does a better job of explaining things but as a manual that's what you get. There used to be a series of books called Magic Lantern but as far as I know there is no plan to have one for the K-5. Which means you are stuck with this forum, so just ask!
The only time I use AF.C is for birds in flight, I think AF.S produces better results as you can never be sure exactly what AF.C is locking onto. I also only use single point focusing, I do not trust the camera to focus on the subject's eye for example if that is what I want. Far too easy for the camera to lock onto the nose or ear or whatever. Some of these errors are covered up when using the kit lens or any lens at smaller apertures, but the DA*16-50mm goes to f/2.8 and at that aperture your depth of focus can get too narrow.