Hopper bottom brakes inoperable

Have you greased them and freed them up?

 

Were the glad hands left exposed when the trailer was stored? Mud dauber pack some putty in the service line?
They are active right now.
If the brakes fully release off the drums and fill the the tanks with the supply line but work slow or no with service that would be my first thought. I always cap them off with dummy hands when unhooked even if for just a day. Keeps dirt and water out.

 

we got into the habit of taping the glad hands on trailers that are going to sit for extended periods, insects would build nests inside the lines and cause grief. could be something decided to set up camp in your service line.

 

With someone help check parking brake functioning, how quick brake shoe release and set with red button push/pull. If it's slow S-cam are seized. Grease and try.

 

I would also say you probably have something blocking the line. Take the supply and or signal lines off the valve and I'd bet you'll find it packed full of junk