Q: iMac won't go to sleep

Thanks for the response, but that didn't work.  I have a standard iMac with wireless keyboard and Magic Mouse.  I put the iMac into sleep mode, and turn off the mouse when I'm done working, and after a few minutes of no activity, the keyboard turns itself off.  What is happening is the Bluetooth Setup Assistant doesn't detect the mouse or keyboard because they've been turned off, and the annoying pop-up comes on, waking up the system.  The pop-up stays on all night and causes a bit of screen "burn", not to mention the annoying hum of the fan.

What DID work is setting up the Bluetooth configuration correctly.  Go to System Preferences/Bluetooth/ Advanced; unclick the settings that say "Open Bluetooth Setup Assistant at startup if no keyboard is detected" and "Open Bluetooth Setup Assistant at startup if no mouse or trackpad is detected."

Now, the iMac goes to sleep when I tell it to go to sleep.  I wish my niece and nephew would do the same...