That's a tough one. Many, many ways around it. My favorites are either to just pile up music that fits the mood into my winamp in a loop, or - sleep on it. Ideas bubble up when I'm only half awake, and the mind works even when you're sleeping.
The following day I'd at least have a lead.
Thinking about it actively all the time is counterproductive because you keep looking for the solutions where they won't be - and that's where you know to look. You need to let your mind wonder.