Reset RAM? Perhaps you've heard about Mac users resetting PRAM?
Parameter RAM and the associated battery is where certain settings are held when the iMac is off or unplugged. This article gives details.
To reset the PRAM (which is a common troubleshooting technique) hold down the Apple, Option P and R keys immediately after the start-up chime. Let them go after you hear the chime again. This article expands.