Can you speed write?
"That's not writing. That's typing," Truman Capote said when he heard how many thousands of words the young Jack Kerouac wrote each day (I'm paraphrasing that quote, but you get the idea). Sometimes, though, you need to just type. The best cure for writer's block is to just sit down at your keyboard, turn on an alarm or timer, and type till the buzzer goes off. You don't edit, you don't correct misspelled words, you don't try to choose the right turn of phrase, or metaphor -- you just type.
If you do this I guarantee you'll turn out a lot of words. Some of them will be utter dreck -- in fact, a lot of them will be utter dreck -- but you'll get your creative juices flowing, and usually you'll find the germ of a good idea in the middle of all those words. Sometimes you get lucky, and a really great idea, or sentence, or paragraph comes out of what you wrote.
When you speed write you turn off the internal critic, that little gremlin inside who constantly tells you you're not good enough, and that the sentence you just typed is stupid, wrong, and will damn you to hell forever if you let anyone see it.
Here's a great site to teach you how to speed write: Write or Die by Dr Wicked. You can set a time limit and a word count, and then you just start typing. If you stop typing before you reach your time limit, there are visual and auditory cues to get you writing again (try the kamikaze mode!).