Chosen Solution
No start but tone sounds. Occasionally thin white n black lines appear on screen. Occasionally multiple tones sound but no start Help Update (10/12/2016) Hi Sry on delay. Lost power from hurricane. iMac will now not start - I do hear the usual 2 tone electronic bizz buzz that precedes the startup bong. Kinda like it wants to but just can’t. A1312 100~240 v,50-60 Hz 4.0A. EMC 2429 I am loathe to buy a new iMac and would love to fix this guy. I have previously replaced the power supply that went bad after a lightening surge. Simon
First Reset your PRAM Here’s how to reset your PRAM: Shut down your machine. Yes, all the way down, not sleep or logging out. Press the power button and then press command-option-p-r. … Hold those keys down until your Mac reboots again and you here the startup chime. Let go of the keys and let your Mac reboot normally. Next, to help narrow the issue, hook up to an external monitor and tell us what you get on that screen. Please give us the Axxx number and EMC number from the bottom of your stand.
Replace the GPU. Sounds like a graphics defect.
