When writers talk about writing, it's only a matter of time before the subject of the muse comes up. What does the term actually mean? In Greek mythology, the word "muse" refers to any of the nine daughters of Zeus and Mnemosyne; each goddess ruled over a specific field of art or science. When an artist today talks about a muse, they mean the source of their inspiration. So asking "where's your muse" is another way of asking "where's your inspiration?"
So, then, the muse. For some writers, it helps to actually visualize their muse as a grumpy man in the next room or three sisters in the basement. Others might use a photograph of their main character or other tangible item that could have been pulled from their story. Some listen to music that their characters would like. Still others claim to not have a muse.
Many moons ago, I used to be one of the latter. I bristled at the notion that motivation could come from something other than myself. Recently, though, I realized I've had a muse all along; it just wasn't easily recognizable because it changed with every story I wrote. During The Gemstone Prophecy trilogy, I imagined a magical stone I could hold in my hand. As "Return of the Black Seraph" happened, I held fast to the desperation and despair my protagonist must feel. For my current short story project, "Gabriel's Wish," I find that I do my best work while listening to the What Women Want movie soundtrack.
Basically, it comes down to this: get out of the story's way. Let it be written how it wants to be written. If that means hand-writing instead of typing or working at a cafe instead of at home or listening to music instead of total silence, do it. And don't question it. Let the writing happen.