iMac won't power on

According to Apple:

If your Mac doesn't seem to turn on after you press the power button, follow these steps:

1. Make sure that your Mac is connected to AC power. If it doesn't have a built-in display, make sure that your external display is connected to power, connected to your Mac, and turned on.
2. Press and hold the power button on your Mac for at least 10 seconds, then release.
3. Every Mac has a power button. On notebook computers that have Touch ID, press and hold Touch ID.
4. If you see no change on your Mac, press and release the power button normally.
5. If your Mac now turns on but stops at some other screen during startup, follow the steps for when your Mac doesn't start up all the way.

If your Mac still doesn't turn on, get live expert assistance by contacting Customer Support by phone or chat:

• Call Apple Support at 1-800-APLCARE. 📞
• International Support. 🌐
• Contact Apple Support. 📝
• Live chat using Messages. 💬

If your Mac doesn't turn on - Apple Support