Sometimes, you have to just write and write and keep on writing. It's okay if its a pure crap and ty. That's what we called 'draft'. And that's why we have editing. If there's a scene in your head, just write it down. Don't worry about grammar, sentence structure or anything. Just write it all, pour it out on the paper/document. When it's all done, go and edit it brilliantly.

Anyway, good luck with your story! :)

The thing that helps me when I get writers block is to listen to music. I get most of my inspiration from music. So if you're writing angst try some sad songs, if you're writing fluff maybe just a typical love song, if you're writing a very descriptive story try songs with artistic lyrics and etc. Try listening to new music too or even watch some movies. This might not work for everybody but I hope it helps. Good luck!