Empty the drawer that's stuck. If the drawer is stuck closed then open the drawer above it and remove the higher drawer by lifting it out of the track once it's fully open. Reach down into the open space and empty the files in the stuck drawer.
Attempt to open and close the drawer that was stuck once the weight is out of it. If the drawer works normally then the problem might be weight related. Even though steelcase file cabinets are meant for heavy weight, too much can still create jamming issues.
Take the stuck drawer out of the file cabinet. Wiggle and pull, using the prybar to gently lever it if the drawer stays stuck. Once the drawer is fully open lift it out of the tracks and turn it over. Examine the rollers that fit into the tracks to see if any of them are stuck or broken. If the rollers all work smoothly, then the problem isn't with them.
Examine the tracks on the inside of the file cabinet. There will be multiple tracks on the left and right side of the drawer to help support extra weight. Make sure that the tracks are held tightly, that they aren't bent out of shape and that there aren't any obstacles or debris in the tracks to stop the drawer from rolling smoothly. If you find a bend in the track then bend it out straight with your prybar. If the track is loose then tighten the screws holding it in place.
Replace the drawer. Open and close it while empty to be sure that it opens and closes smoothly. Gradually add weight to the file cabinet drawer and keep opening and closing it to check the smoothness of the track.