I never get stuck composing music. Music always just flows for me.
Maybe it will help if you play a piece similar to the style you are composing in and then just keep on going according to what you feel and start composing from there.
In my opinion Kapustin is a really innovative composer who is highly underrated. His works are easy to understand and comprehend and yet his music is highly innovative and every work is fresh. He has taken fugues to a new level and dimension.