Unable to fix the "Blinking Floppy Disk" issue on iMac G3

Welcome Andy!

That startup result, as you have likely already discovered, means the boot process cannot find a valid operating system:

If your Mac starts up to a question mark - Apple Support

I have MacOS 9.2 installed on the internal HDD...

How did you install OS9? Pre-OSX versions usually required "system enablers" specific to the computer, and the only valid reinstall options were:

• the same gray system install/restore disks that came with the computer
• a full retail install copy of macOS ( had all possible combos of enablers)

Even the gray disks from a similar iMac was unlikely to work even if they came from the same model iMac but having a different logic board revision (common back for a Rev B board to require different enablers than a Rev C.)

This:

..when I go to the boot menu and select "Macintosh HD" it loads for a second and goes straight to a blinking floppy disk and stays there

is what suggests to me an enabler issue.

Burned disks with downloaded versions iof OS9 almost never worked on old Macs. Same with bootable flash drives.

So it sounds like a problem with the source of the OS you installed. Did your boss give you the disk set that came with the computer?

We may be able to narrow the search for answers if you tell us if the optical drive is tray-loading or slot-loading. That physical change represented a change in logic board design and firmware, so might help us better help you.