iMac G5 Won't Start

My iMac G5 seemed to be running good. I then unplugged it from power for a few days. When I connected it back to power and tried to turn it back on the cooling fan immediately went to full speed, there were three loud beeps, the white front power light flashes 3 times pauses and then follows this sequence again. Also the screen remains dark. It will stay in this state of limbo with the cooling fan racing until I hold the power button in long enough for it to turn off. Does anyone have an idea of what the problem could be?