The aperture in the lens looks like this: http://www.edinphoto.org.uk/0_EX/0_exposure_talk_pentax_lens_042901_1024.jpg

The hexagon shape thing (though it might have more sides depending on the specific lens)

If that's not getting wider or narrower while you turn the aperture ring then your aperture is definitely stuck and its definitely a warranty repair.

Hey, sorry I haven't gotten back to you sooner. I haven't been on this forum in a looong time.

If your lens just magically stopped working and it seems dark and won't focus on anything, take it off the camera and try changing aperture manually (I seem to remember that that lens had a manual aperture ring on it?). If you can't see anything moving in the lens and it doesn't get brighter, then you almost certainly have a stuck aperture, in which case it should be a warranty repair.