Check the battery, and check your Apple Watch charger
One common reason an Apple Watch won't turn on is simply that the battery is dead. Connect the Watch to its charger, and if that doesn't work, make sure you try a different charging cable and charger to see if your charger is faulty.
If your Apple Watch is still unresponsive after you try to power it with several different chargers, then move on to the next solution.
Perform a force restart
Your Apple Watch may be frozen. Forcing it to restart can unfreeze the operating system and get things working again.
Press and hold the two buttons (the larger, circular Digital Crown and the smaller oblong Side Button) simultaneously for 10 to 15 seconds.
After the Apple logo appears, release the buttons and wait another few seconds. When the watch turns back on, it should work smoothly again.
Read more: How to turn your Apple Watch on and off, or force-restart it for troubleshooting
Turn off Power Reserve mode
Your Apple Watch has a Power Reserve setting that, as the name implies, saves power. In this mode, only the time will display, and the watch will not unlock.
To exit this mode, press and hold the Side Button (thinner, oblong) for about 7 to 10 seconds. When the Apple logo appears, the watch is rebooting into its regular mode.
Turn off the Screen Curtain
The Screen Curtain mode keeps your Apple Watch's face darkened even when it's operating normally, only allowing interaction via voice.
To turn off the Screen Curtain, open the Apple Watch app on your iPhone, then go to the General tab. From there, tap "Accessibility," then go to "VoiceOver." Finally, toggle Screen Curtain off (the button will be on the left).
The Apple Watch should work normally again.
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