My iMac has power but shuts itself off during boot. Now what?

I purchased an iMac G3 (M5521 from 2000) that was tested and working, and then after transport home in my car I plugged it in and it does not boot. The most that happens after I press the power button is a faint popping noise from the left speaker, followed 1 second later by a faint beep and crackling sound from the back (like a CRT after shutting off). No power button LED light, no chime, no POST beeps, nothing on the monitor. I can repeatedly press the button and the same thing happens.

Following the iMac G3 service manual, I tested the logic board, down converter, and the PAV board fuse, and everything is working! Voltages present and fuse not blown. Now what do I do?