Minolta AF 24-85mm f/3.5-4.5 won't focus (assistance appreciated)

Okay... I have a problem with my AF 24-85mm f/3.5-4.5. It has stopped auto-focusing. The manual focus works fine, but when I have it in autofocus, it whirrs, but does not focus.

 

For background: I had it on a Maxxum XTSi, when I went out to shoot some early spring shots in the local state park when the sun came out. I did not drop or knock it in any way, and the switch back from AF to MF seemed perfectly fine. The problem arose when I put on a CPL filter. It did not want to sit on the threads, but eventually screwed-in just fine. But then, the camera would not autofocus. I removed the filter, and it still would not autofocus. My 70-210 beercan works perfectly, though. So the problem is with the 24-85 and not the body. Any ideas? Did I somehow damage the focusing mechanism when I put on the filter?

You're certain it's a circular polarizing filter, and not a linear polarizing filter?

It's certainly a Hoya CPL. It briefly crossed my mind that a linear polarizer might interfere with the focusing sensor, but that isn't the case. Besides, it won't focus with the filter removed. The more I think about it, the more I think that I might have inadvertently jarred whatever linkage there is in the focusing mechanism when I initially had trouble with the filter. I didn't force anything, but I wonder if something got knocked out of place. Does anyone know if this might be serviceable (I'm fairly handy)?

When you turn the manual focus ring with the lens off the camera, you should see the focus coupling in the lens mount spinning at the same time. If not, something mechanical is disconnected.