Cannot power up and shows flashing folder symbol (?)

My iMac G5 suddenly could not power up.

It gives the opening sound, briefly flashes a grey screen, but then shows a folder with an alternately flashing Apple "face" and question mark.

I have read many posts and followed instructions to re-set the PRAM (successfully) and also the SMU. All to no avail.

Is there a meaning to the folder icon to indicate the possible fault?

I am in an Australian country town, with no access to an Apple service centre.

I am aware that power and capacitor problems are common to the G5, but would be grateful if you could advise anything further.