There is nothing to be gained by giving in to that sense of hopelessness. It wears you down even more. You are going to feel worse than ever. Once you reach the point where you can do nothing to ameliorate the situation, then use it. Pull every bit out. Get hold of the disappointment and wring everything out of it that you can. Emotions such as anger, hatred, rage, despair are going to fuel your writing and inject it with an extra ingredient - passion.
So heat your words with the flames from your soul.