Basement sliding glass window (Pella) - how to remove the pane opposite of the sash
I cannot speak for all sliding windows but on mine the fixed section has some bracket things in the center corners top and bottom that keep it in place and prevent it from being lifted up to clear the lower track. 

Removal on most of these involves lifting to clear the track on the bottom and then swinging the bottom away from the frame. Many times the movable section has to be removed before the fixed section can be removed. On mine both sections have to be removed toward the inside.