Sometimes, you find yourself in the mood to start that essay early, getting it ready well ahead of next week's deadline. So you sit down, begin typing and, for some reason, find yourself unable to put anything down. You're stuck and you don't know how to get out of it. Here are a few ideas:
Don't write. Instead of writing your essay, just assemble an outline based on your research. If you're familiar with mind-mapping tools, you can put one together specifically for it. Just because the words won't come doesn't mean you have to stay idle - pre-writing instruments, such as these, can do immense things to make writing easier when you're ready.
Write disjointed sentences. If you can't write a sensible essay yet (you're blocked), then put down disjointed sentences. Anything that approximates (even very poorly) what you want to say will do. You might be surprised at how much of the text you produce this way will actually become usable in your final draft.
Plagiarize. Sometimes, using others' words can get the ball rolling. When you do this, make sure to put markers on portions of the text that you ripped off directly, so that you can rewrite them later (while you proofread or use your essay writing checker). The last thing you want is to turn in a finished essay that contain sentences directly lifted from other people's materials - that just puts the rest of your hard work in bad light.
When you're stuck, getting over it is usually about finding things that allow you to get a headstart. Once you're over the hump, the words can flow.