It's a strange phenomenon, but sometimes stories refuse to be written. You can have it all plotted and planned, the opening scene is already playing like a movie inside your head. But when the time comes to commit your story is paper or pixels, it refuses to come out. The damn thing develops a mind of its own and your writing grinds to a halt, frustrated, lifeless, or empty.
Bloody annoying, that's what it is. When this happens I tend to think of it as my subconscious sending me messages. [We had a weird relationship, me and my subconscious - a bit like Dexter and his Dark Passenger.] What's it trying to say? You're not ready to write this story yet. You don't know your characters well enough, or the factual basis for your narrative. Maybe you need to do more research. Or maybe it's just a craphouse idea that needs time to simmer.
Forcing a story out when it doesn't want to be written is never pretty. Watching paint dry while being whipped with barbed wire might be more fun. And the results are never much cop. Far better, if you can, to do something else. Write a different story. Make something else up. Do some research, go for a walk, visit a gallery, read a book. But that's not always possible.
Some story documents have to be written, whether or not you [or your subconscious] is ready to write them. Deadlines are deadlines, especially when money or marks or your mortgage is at stake. But there's no shame in admitting a story isn't working. You may not be able to write it as well as you'd like now, but that doesn't mean you can write it down and fix it later.
Sometimes it's the tyranny of perfectionism that's crushing your work. My advice? Get over it. No first draft is perfect, much as I'd like mine to be. The rewrite is where lumps of coal get polished to reveal [hopefully] the diamond within. Sometimes you need to stick that story on a shelf in your brain and come back to it later, give your subconscious time to think.
Stories can be like a good chilli [or curry, if you prefer that]. You cook it one night and it tastes fine. You reheat leftovers the next night and it tastes great, even better. Why? The spices and sauce have had time to seep deeper into the protein, creating a richer flavour. Leaving a story alone to marinade inside your mind can have a similar effect.
For Doctors I've written story of the day ideas out, only to realise they're not there yet. I've got all the ingredients, but haven't figured out the correct proportions to get it just so. Better to come back in a few days [or months] and see what my brain can devise that'll improve on the first attempt. Time makes a wine, and it's the same with some stories. Onwards!