My K20D will not autofocus or release the shutter. A 16-45 f4 PENTAX lens is mounted. Help!

1) Remove and replace the lens making sure it "clicks" in place properly

2) check the focus switch by the lens mount is set to AF.S

3) Test with another lens if possible  to see if its the camera or lens at fault

If the problem persists only with the 16-45:

a) Check to see if any of the contacts are dirty or stuck

If all is clean and moving, then you could have a fualty lens

If the problem persists even with another lens:

a) make sure the camera body contacts are clean

b), check in the camera custom menu "C" , and in options 13 and 14 to make sure the AF button is properly set to autofocus / shutter release

If nothing above works, then you might have a genuine camera body problem.

Good luck