Originally posted by WhatsMyNameAD67
This is a common issue with well used 67s. Have you checked to see if the mirror is also locked up? I read where Zelig slapped his on the side

to release and reset the internal magnet. Weird, but it did work. Here’s an article:
Pentax 67II winding lever stuck - PentaxForums.com
The camera being referred to in this post is a Pentax 67, the original 67,
not the 67II which proceeded it.
Internet nonsense about slapping, banging and generally mistreating these cameras is one of the reasons the market is seeing so many of these cameras with intractable faults and damage.
With the lever stuck, get a toothpick and depress the recessed reset button to the left of the mirror box. Then fire the shutter and attempt to wind the lever through its full cycle. I have seen this procedure done on an older 6x7 and it worked, but it then highlighted a fault in the winding mechanism, again, something that is common in the older 6x7 cameras than the newer (1989 onward) 67. It is worth trying this just to see if it clears the jam.
When winding the 67, the wind-on stroke must be completed in one fell-swoop, not broken into one or two small efforts, just one big wind. The lever must then be guided back to its resting position flush with the case, never allowed to 'flap' back.
Try the reset procedure and see what happens.