My watch screen is black

See this for an Apple Watch that won't turn on. If your Apple Watch won't charge or it won't turn on - Apple Support

If that does not help, use the Get Support link at the top of the page here to contact Apple Support for service.

Does the screen come on if you press the Digital Crown, or tap on the screen? Try resetting the Watch. Press and hold the Digital Crown and power button together until you see the Apple logo and then release. See if that helps.