Ice box room upstairs
Ductwork usually has a vent damper below where it rises up from the basement. If it is a manual damper, it probably looks like a wing nut see this picture

It's possible most of the dampers are closed or partially closed, and the really cold room is fully open. 

If you have dampers like this, you can loosen the wing nut and adjust the damper with a flat screwdriver. Usually the blade orientation matches the orientation of the damper. So if the blade is parallel to the duct, it is fully open.