unlocking seat belt 2000 ford Taurus ( no accident)

I'm not familiar with that specific one, however ones that I have worked on have a plastic cover on the end that covers the cam and gear. If yours is similar, then move the cam.

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Is it back in the car now, or still sitting on the kitchen table?

There's usually an "inertia" lock of some kind inside that responds to sharp movements of the car (and sometimes really steep hills), and locks the reel. If it's out of the car, and you're not holding it in the same position as when it's installed, gravity can cause the mechanism to shift to the "lockup" position. Holding it in the correct orientation and giving it a couple of thumps should unlock it.