Dead iMac G3

1. The G3 iMac is considered an antique.
2. You should never buy any iMac from E-Bay.

You should consider buying a new or a much newer refurbished iMac from a reputable seller.

https://eshop.macsales.com/configure-my-mac/imac

https://www.macofalltrades.com/apple-desktops/?

As someone who owned several (400 MHz) G3 iMacs, even buying one locally is no guarantee as to the number of hours of prior use or how many it will provide you. Sooner or later, the design flaw catches up with most of them. Without warning and following 4 months of non-use, I plugged in one of mine and pressed the power button, only to hear the characteristic "pffff" sound that others have described following PAV board failure. It's disheartening to e-cycle something that worked the previous time and suddenly became non-functional, especially when it's in good cosmetic condition. The PAV board is such an integral part of the slot-loading iMacs and replacing it is dangerous for anyone who's untrained in CRT repairs. When accessing it, cracking the plastic housing when separating the sections is also a possibility. Paying a tech to replace it would only be cost-effective if the part were new. Any pulled/used boards that you find online would eventually fail for the same reason. Here's what the PAV board looks like:

+1 on den.thed's info.

If a Graphite, I believe yours is the "DV" version with a slot-load optical drive. The slot-loading G3 iMacs had serious weak spot that does not help them age gracefully—the PAV board.

PAV stands for "power, analog, video" and is exposed to high heat where it sits. Of course, Zen-like, the G3 iMac had passive convection cooling instead of a proper fan system. The PAV board was heated by just about every bit of kit under it and boards failed, especially if used in high-temp environments.

We experienced similar symptoms with a Summer 2000 G3 our daughter used in an 85F+ apartment with no chilled air. If yours is complaining about the heat but not damaged, there is a workaround. If you do not mind making the iMac look like a prop from the movie "Men in Black II," ( remember the "Deneuralizer"?), you can add an external 120mm fan across the top vents. Set it so it pulls air up and out of the computer. Forcing air in from the bottom is far less effective.

If the PAV board has been fully baked or fried, that fix won't help. Serve with a nice Béarnaise sauce and a glass of Riesling. 😉

You're welcome.