The trick — and it’s imperfect and can take a while, but — is simply to write something else. Don’t let your hands go cold. Don’t let yourself stop thinking. Shift to something different. It’s about letting your backbrain chew on the problems while your frontbrain is amused by the new and shiny things. Write something else. Anything else. Either you’ll solve the problem in the background, or get the taste back for what you’re stuck on — or, guess what, maybe that whole thing was dead and you were just shoving electrodes up it to make it twitch in an awful semblance of life the whole time.