Condolences!
The DoF button actuates the aperture mechanism. Perhaps some part of the electronics or the mechanism has failed. You want look closely at the aperute actuator for any kinds of damage. But before you cry "dreaded aperture block failure," see if it works with a different lens. It's a long-shot but perhaps a stiff aperture lever on one particular lens is blocking the DoF/aperture cycle from completing properly. If it happens with more than one lens, then it's probably a fault with the camera.
Good luck!
(P.S. I must admit I live vicariously through your marvelous acquisitions.
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