I am diagnosing this for my school. There is a blueberry iMac that when you try to turn it on, nothing happens. The green power light comes on, but nothing else
This is not an uncommon problem. I've seen it more than once, usually on machines that have been having problems with the display for a while. In my experience, it's been a bad component related to the HV circuitry. There are a few things that can cause it (cracked solder joints, bad flyback transformer, leaking capacitors, etc), so I can't tell you exactly what to look for. My bondi did this, too, and the culprit was cracked solder joints on the flyback transformer. Resoldering those connections did the trick for me, but like I said, any number of failures in the power supply/CRT HV circuitry can cause these problems.