G4 Cube power light was flashing before it died, what does this mean?

There are a few links for additional information in this other ASC reply thread:

Re: Keeping my old powermac G4 cube...

Hopefully you can get your G4 Cube to function ~ or, arise from apparent coma.

Good luck & happy computing! 🙂

Hard to tell what is the cause of this issue, nor what detailed troubleshooting steps

may be helpful to troubleshoot or bring it back to life. One of the items to consider

replacement on an older Mac, is the PRAM clock battery; it can affect startup and

also system runtime considerations. ~ There may have been a power supply failure.

To reset the power management unit would be part of a troubleshooting scheme;

also a pram-reset. Given each different Mac series tended to have certain various

power management unit names and processes to re-set them, to find what your

G4 Cube has, to use it to try a PMU (or other name) power reset; and troubleshoot.

So these few items could evolve into other steps to help troubleshoot the issue.

If you have an original (copy) of Service Manual, they could be helpful given some

items that may be problematic. Back in the day, part of an official repair included

swapping known-good parts, at a certain point in the troubleshooting, as a fix...

A link to perhaps helpful extra information (a PDF) this can be saved for offline use:

[ Here's a service source to G4 Cube manual ]

Given the vintage, that opportunity to grab a known-good replacement part off a

shelf, isn't available to most casual users. Old-stock/new may also be vintage/rare.

There may be some hints among iFixit repair guide specific to this singular model;

and other items among specifications in everymac.com site. Info; and then parts?

Good luck & happy trails! 🙂