Imac24 will not turn on

After trying kai-k's recommendation one more thing you can try if still unable to turn on is: unplug the power cord from the back of the iMac for about 15-20 seconds. Plug it back in and try turning it on with the Power Button.

If that works it's an indication of a failing power supply and the iMac may shut down at any time.

Hi,

Following article could help your issue.

If your Mac doesn't turn on - Apple Support