Dimmer stopped working
Assuming that the bulb isn't burned out, the dimmer failed. It happens.
We installed simple incandescent dimmers for all of our lights when we moved into our house 25+ years ago. We've replaced every single one of them at least once. Maybe it's because we bought the cheapest one on the shelf at our local big-box store...
Replace the dimmer.
Cautionary note:
Be sure to:

Turn the power off at the breaker

The easiest way to know you've got the right breaker is for the light to go out, but since the light's already out...
Pick up a non-contact voltage detector while you're getting the new dimmer. For $15 or less it can save your life.


Have the new dimmer handy before removing any wiring

When you've got the old dimmer out of the wall, but BEFORE removing any wiring:

Grab your cell phone &amp; take good, clear, focused pictures of all the wiring connections.
Take good, clear, focused pics of any extra wiring in the back of the box


If you're not clear on how to rewire the dimmer based on the new one's instructions and what you're seeing in the box, come ask a new question here before disconnecting anything.

Include all your good, clear, focused pics
Include the make/model of the new dimmer. A link to the mfgr site (and instruction PDF) is always appreciated



It's a lot easier to ask a &quot;stupid&quot; question than it is to rewire it wrong which could damage the new dimmer, the fixture/bulbs, or you.