Originally Posted by back alley
Sounds very much like the rack is stuck, in that case. Though I would suggest ensuring the shutter is set to a high speed and the timer has not been engaged. These are so well known for jamming the rack it's almost certainly the case—but in the interests of being thorough it's worth ensuring the shutter itself has not failed to release due to a sticking escapement or stuck timer.
The good news is the cover comes off quite easily, and the film wind system is one of the most straightforward you're likely to find on a 35mm camera. Removing the rack, cleaning and lubricating it, and then adjusting the tension on the racks spring (you may well need to bend it carefully to compensate for it reducing in strength due to age) and it will probably be a goer again.
The bad news is the spring for the advance lever coils around a drum under the lever and has to be pre-tensioned before the wind lever can be re-attached. And the lever can't, obviously, be replaced until the cover is back on. Meaning you need to keep the spring tensioned while the cover is fitted and the lever replaced. From memory, fitting a couple of the fastening screws for the lever keeps the plot positioned while the cover goes on—but you then need to remove them, mount the wind lever back on, and fasten the screws—all while the drum underneath just wants to unwind the spring.
If you have three hands it's almost easy to achieve. Otherwise it's quite fiddly but not complicated. I can do one pretty easy now after a bit of practice. It usually boils down to introducing the lever to the boss of the drum with a thin screwdriver inserted through one of the holes for the mounting screws. This is then fitted inside one of the still vacant threads for the lever screws, so the driver can jam the drum long enough for you to fasten one of the other lever securing screws, before the wind spring wins and it all backs off too far. The drum sits on the wind shaft above a stepped cam plate which a spring loaded pin inside the drum catches every time it meets the "step". Whilst you're stopping the wind spring from unwinding the drum, you also need to ensure the drum does not slide up the shaft or the pin spring may pop out of place.
All up it's a pretty easy repair but there are some tedious aspects as outlined above. Honestly getting the wind lever and cover on is harder than actually sorting the rack in my experience, which is an elementary piece of mechanics, the operation of which is self explanatory.
Can provide more info and pics—have not heard back re my previously prepared instructions yet but have all source material on file, so if need be can write it out again.