Q: How to fix blinking folder/question mark upon startup.

It sounds like the disk drive is either corrupt or dead so that they Mac is unable to find a system file to boot from.

You are going to have to get the CD for that Mac if you want to do anything with and possibly a new disk drive.

If you haven't found info on how to look into the take-apart and troubleshooting

there are some online resources; most require some degree of technical skill...

And most modern Apple resellers may not have qualified persons on-staff now

to do that kind of work. Parts can also be a problem; however a replacement

hard disk drive (IDE/ATA or PATA) may still be available if you look long enough.

You can see some ideas on the inside features of this series, from the details

shown in these limited iFixit repair guides for iMac G4; several models exist.

https://www.ifixit.com/Device/iMac_G4

• iMac G4 Take-apart for Drive, RAM, and PRAM Battery upgrades:

http://www.xlr8yourmac.com/systems/imac_g4/imacg4_takeapart.html

• Mr Totes iMac G4 take-apart (appears to be a 17-inch 1.25GHz USB2.0 model)

http://www.mrtotes.co.uk/page1/page1.html

If your model proves to be one with USB2.0 and other hardware 1.25GHz, etc:

After sitting around unplugged awhile, the PRAM battery or clock battery likely

is bad or flat. These do not recharge, and need replacement. This can directly

affect the ability of the computer to start up. Also, if there is a power issue

a qualified tech who knows these, should be able to test the power supply by

use of small test ports, for use with multi-meter, in the bay under the metal disc

bottom plate. Next to the location of the AirPort card; that may not be present.

Later model iMac G4 used 'AirPort Extreme' wireless card, not interchangeable.

The correct battery would be a 3.6V 1/2 AA Lithium cell, and this one does

not have solder-tabs, it friction-fits in a battery holder. And getting to it will

require the tools and understanding of how the unit is supposed to work as

well as following steps to get it apart & then clean off the old thermal paste

from the cooling conduits to the PPC G4 processor, and before putting it back

together again, replenish new thermal paste to the contact points of the

processor's cooling apparatus. But not too much.

PRAM Battery, example:

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

There should be a serial number on the bottom plate, inscribed along with info

about Apple computer, in the metal; this could be used in an online Lookup

database, to see what exact model build version the one you have actually is.

• Mac Serial Number info - Look up your Apple Serial Number:

https://www.powerbookmedic.com/identify-mac-serial.php

Sources such as everymac.com have some info about these models & others;

the download app from http://mactracker.ca can help with Mac specifications.

Since I have a few of these computers sitting around in various states of repair

or lacking certain known parts to work correctly, I haven't been terribly interested

in fixing these at this time. One was included with another, as a parts machine;

it had an original box, the working one was similar. But it developed a problem

with the optical drive; however to take one apart to extract a used drive for the

other, and then re-applying thermal paste (don't have) so the cooling conduits

for the processor would be correctly re-connected, and other bits, is not in my

time budget. I do have two Mini Macs, a Last G4 Mini 1.5GHz and a Late 2012

plus a few portables that work but could use repair; some technical level not in

my ability and I haven't a repair space anymore, as I once did.

Anyway, hopefully you can work out the details and locate the original install

system discs; or at least the supported OS X retail versions for the vintage

model computers you have. The iMac G4 800MHz cannot directly run Leopard

10.5, so it would need to have the retail later version 10.4 DVD. If the unit is

older, it may not have had a Combo optical drive; so it may have shipped with

a 4-CD set for the older original operating system and applications kit. Rare.

Gray-label software install-restore kits are not interchangeable between models.

In any event...

Good luck & happy computing!

eBay is your friend. You can find OSX 1.4 or 1.5 (depending on exact model) cheap on there.

That's 10.4 Tiger or 10.5 Leopard. All iMac g4' s should run any version of Tiger or Leopard.

You could get an external firewire drive, if you do not want to mess with replacing the internal drive. You can even buy a new drive.  You will need a firewire 800 to firewire 400 adapter.  Works well in my imac g3 600.

http://eshop.macsales.com/shop/external-drives/

I recommend a powered external drive.  I would not recommend going above a 2t external drive. I know 5 & 6 do not work.

external usb drive will not boot.

R