I was working on my iMac and all of a sudden the screen goes black and it never has powered on from then, I opened it up and had a look at the diagnostic LED’s and only led1 turns on when connected to power. When I press the power button I can hear the hdd blowing, while no other led it being lit up. If I hold the power button the hdd beeps very silent and stopt blowing. Can anyone help me? Could it be the power supply?