Many thanks to one and all who took time to write various suggestions. When replies came I was hit right over the head with my failing brain and the obvious aging battery. Battery is original and I believe this unit was bought in 2000 or 2001. I will replace it first, then move on to cuda button before replacing power supply. If above fails to provide requisite fix it is Good Bye iMac since replacing the flyback transformer is well above my abilities. Ken Philbrick