Sounds like there's something jammed or bent in the mount mechanism of the camera. Probably something with the aperture mechanism - what you describe is due to the camera essentially being in stop down mode the whole time.
I just posted a link to the manual in another thread... over in lenses,
Pentax Super Program Manual
Look for the DOF preview lever (p.50) and see if it moves - try first without lens and look to see what moves inside the mount. This lever may be jammed and this COULD cause all your trouble. Try this in the different exposure modes too - the manual says DOF preview won't work in program or Tv. Try with a lens on but in manual or Av mode, and see if the switch moves.
Oh, and since you have a working K1000, look at how the aperture lever on it moves, your other camera should be similar.
If that doesn't solve it, can you return the camera? It will need repair.