Power wont turn Back on.

Yesterday my power went out so my Imac must of been on so i tried to turn it on later thru out the day it wont turn on! Looked up some Details i can try so it would turn on Like Reseting the SMC that did't also Removed the RAMS that also did't work. so all there is left is if i need a new Power Supply or the Logic BOARD probably went bad well i hope not. i hear a noise on left top Front side AND on the right top back side but you have to put your Ear close to it. What does that mean? PLEASE HELP. i hope is just that i need a new {power Supply}. Oh and the noise only comes on when i plug it on (well Duh).