Paper, lots of paper

I am eager to get to my computer to start on my latest idea

Get started in little ways before you “start writing”.

Similar to the Answer by GGx, I suggest using pen-and-paper rather than computer to get started.

My key point here is that brainstorming and planning are separate phases from drafting ("writing"). Drafting is done at the computer when you are generating your prose. But before that you must have ideas, directions, doodles, outlines, and such from which to generate your prose.

I myself am doing technical writing rather than fiction, but I suspect the process is similar. I walk away from the computer, literally, going to a coffee-shop or friend’s home. I carry a certain small backpack or bag with loose plain-white paper, a notebook, a fine-paper pad, and an inexpensive but enjoyable fountain pen. I pull out of my pocket some scraps of paper or napkins with a title, key phrases, or blips of ideas. From that I sketch, doodle, and draw my own version of mind maps. I do some research on an iPad. I make a list of resources to consult again later. I jot down every thought, every point, that might be useful.

Eventually I begin to organize those points, evolving into a loose outline.

From there I make rough cuts on the loose-leaf paper (or index cards). I use loose-leaf so I can shuffle to change order or replace entire pages. I switch back-and-forth from the loose-leaf pile to all the other material to make sure I included all the good nuggets, or to redirect myself if I lose my way.

Only after the pile of loose-leaf pieces come together as some kind of a whole do I approach the computer. What eventually comes out of the computer is always substantially altered, but still basically formed from the foundation laid down on paper.

as soon as I see that blank page

Notice the trick I devised: At no time did I stare at “a blank page”.

Another benefit… Drafting is just plain hard work, often a drudgery, like dragging boots through mud. One thing gets me through that: My stubbornness kicks in, refusing to waste all that time, thought, and energy invested in those brainstorming and planning phases.

Whatever process you discover for yourself, I believe the key is separating the phases of brain-storming, planning, drafting, and editing. Trying to wear more than one of those hats at the same time is what kills creativity and drains energy.