No matter what I do, the iMac insists on booting up into the login screen, which will not accept the login password which I am 80% sure is correct. It was a very sophisticated, high-security password which my wife remembered without prompting: "12345". Given that the password hint that appears after three attempts is "123" there is a good chance that she remembers correctly.

I cannot get into recovery mode.

That worked, I can now access the hard drive of the old iMac from SWMBO's newer, bigger iMac. But... where to I go from there?

I would like to get this old iMac into workable condition so I can donate/sell it to someone who might make use of it. The screen is more readable than I remembered, there are about two dozen colorful vertical lines down it, but each line is only one pixel wide and the screen, while annoying, is readable.

I selected Utilities --> Terminal, got the $ prompt, typed "resetpassword" and got the message "command not found".

So, ideally, I would like to completely erase the disk, then install a fresh operating system in it, whatever this old iMac can support, without a login password.

What do I do to accomplish this, given that my only access at present is through the Firewire cable connecting the two iMacs together?

tanstaafl.