First of all, Noob imac owner here. I was just handed down an old imac g3 400mhz desktop that doesn't power at all. When hitting the power button on the unit or keyboard, the units screen makes a noise. No hard drive or green light comes on at all. At dead silence in the room, i can hear the screen flicker, like a tv would come on. I went to go about and read a few problems before, replaced the battery and even tried a new power cord. Any Ideas?