Why Doesn't My iMac Power On?
If your iMac is not showing a picture, getting power, or displaying signs of any hardware sounds then you should follow these troubleshooting steps.
First check the electrical outlet you are using by plugging another device into it. Doublecheck that any surge protector you might be using is also working. Finally make sure that the connection between your electrical outlet and computer is firm.
Unplug all peripherals connected to your iMac like printers, hard drives, or other input devices. Then try starting up your iMac again.
If you are still experiencing startup issues, you should try to reset the System Management Controller (SMC). Find instructions for resetting the SMC.
Other other possible culprit for startup issues involves faulty hardware inside your iMac. If you have recently added new hardware like a hard drive or RAM, check to make sure everything is connected correctly and that it isn't Incompatible with your specific iMac model. You can also try removing and then reinstalling the RAM in your computer.
If you are still unable to start up your iMac after trying each of the steps above, you might want to make an appointment with the Apple Store Genius Bar or at an Authorized Apple Service Provider. And remember, you can use the Genius Bar and all the benefits of the Apple Store even if you didn't buy your Mac there.