Emac died

If the eMac has been off wall power for some time, the internal back-up battery (or "PRAM" battery) is surely deader that dirt. A dead PRAM battery can cause startup issues.You can get a replacement battery for under US$5 online. Radio Shack (Tandy outside the US) has the proper battery as part number 23-026 but it will cost US$15-20.

You access the battery through the same door on the bottom of the case through which you access the RAM modules. Instructions: How to Replace the Backup Battery

...so I decided to quit and start up from a Leopard start up disk

Was the Leopard disk a black one with purple highlights like this:

or is it a gray disk from another Mac model. The latter seldom works.

Some eMac have a near fatal logic board fault that can cause startup issues. Without posting your serial number, see if it falls within these ranges of numbers:

• G8412xxxxxx- G8520xxxxxx
• YM412xxxxxx - YM520xxxxxx
• VM440xxxxxx - VM516xxxxxx

As the computer will not start, you'll need this article that shows you how to find the number:

How to locate the serial number and identify your model

If you find your eMac falls in the affected ranges, I can give further info on how to do a visual check to see if the problem exists.

If you have a bad logic board, the cost to replace is about 3-4X what a used eMac is worth in working condition.

Are you sure the eMac tripped the power circuit and not something else?

Even if the PSU went bad, I don't think it would draw/spike enough power to trip an electrical circuit.

Not absolutely sure on this, though. It might.

Generally speaking, computers are a low wattage device.

Are there any other parts of the room or home that share that circuit from the electrical box?

High draw devices like refrigerators, air conditioners, etc. of that nature?

Plugging in the eMac into a circuit line share by a high wattage draw device may have tripped the electrical circuit.

Was your eMac on a power strip at all or direct to wall power.

Computers should be a some sort of power filtering/power/lightning protection strip.

That fact that your eMac started at all with a dead PRAM battery may have been a fluke.

The PRAM battery may have had just enough power left in it to initiate one last power up of your eMac before your eMac gave up the ghost.

Usually, If the PRAM battery is dead, a Mac will not power or even attempt a startup.

I know where a replacement battery goes

A lot of people posting here don't. We have to assume a worst-case scenario when we don't know the level of tech savvy of the poster.

My Leopard disk is as per your visual

I had to ask because you wouldn't believe the number of posters who try to use the disks from an Intel Mac to install an OS on a PPC Mac.

Another thought,

Even if something did happen to your eMac, there won't be any way to know for sure until you get a replacement PRAM battery.

Without mains power to keep the PRAM battery charged, PRAM batteries last a very short time on their own.

expensing how depleted the battery was already depleted when the eMac was stores, they last anywhere from a say one month to only a few days.

Now that the PRAM battery is completely dead now, your eMac will not power up no matter what you try.

It's a $4 U.S. item.

Purchase a new one from here.

http://eshop.macsales.com/item/Newer%20Technology/BAA36VPRAM/

Put it into your eMac, find, borrow, purchase a good, relaible power strip, plug the strip into the mains socket, and plug your eMac into the strip and see if it will power up.

If it doesn't power up with a new PRAM battery, then we will all know for sure then that something in your eMac got fried.

More than likely the PSU.