If it has been sitting open for awhile, it is possible the chain that runs from the upper crank to the lower one has rusted to the point the links have frozen. It's like a bicycle chain. The little key on next to the lower point is the release key for a locking rachet lever. If it is rotated to far counterclockwise, it will not hold the locking rachet away from the lower sprocket and could fall out. There should be a small screw and spacer from preventing the key from turning too far. It has to be positioned so the upper arm of the key is pointing to about the 1 oclock position. I just posted some pictures of the key in another post.
Here's a picture of the crank mechanism behind the front panel.
Top view of the rachet assembly
Bottom view of the assembly
Hope these help you .