Chosen Solution
iMac went dead, none of the 4 diagnostic led’s lit up. After replacing power supply, hear 3 short beeps that continue repeating until I turn off the computer. When first plugged in, diagnostic lite one illuminates, but when turned on, lite #2 illuminates but the beeping begins.
Here’s a good reference on what the tone codes mean If your Mac beeps during startup From what you describe you have one or more bad RAM SO-DIMM’s.