Is this a non-tilt window? If so, it's possible you have a builder's grade window, which is actually not meant to be removed. It's frustrating, but we have a workaround.
With someone holding up the window, you will need to disconnect the tip of the balance from the sash. Then, close the sash, unscrew the balance at the top, and pull it out.
Let me know if you have any more questions.