iMac very sluggish

I'm a PC consultant who was called out to see an iMac - one of the early ones - that had become very sluggish. It would not read the CD drive, would not do a back-up and when it booted up there was a Question Mark (?) icon that appeared first.
In looking at help, it stated that if you see a ? on boot up you should depress the Option Key, which was nowhere to be found on the keyboard.

I ran the Apple Hardware Test and it passed everything except for AirPort which is not present.

I tried to find the equivalent of a Disk Cleanup utility or a Control Panel but couldn't.

So I left without being much help

Would anyone suggest what steps could be taken to a) first back up the important files to a CD and b) cleanup the iMac so it is no longer exrememly sluggish - or is it at the end of its life?

BTW, its running OS 9

? on startup normaly means that it cannot find the startup disk. hold down the option (alt) key during startup and you will see avalable startup disks. then yoiu can shoose one with arrow keys. my guess is someone shanged startup disk preferences.
you can also try to boot from os 9 cd. hold down C key at startup.

If it is running in OS9 then it would be a good idea to run Norton's 'Disk Doctor' and then 'Speed disk'. Don't run it if the system is OSX as Norton tends to do more damage than good to OSX (New versions than system works 3 maybe different)
The problem that its having (as Mac-simus says) is finding the startup disk, this is a typical problem for old imacs that have had a larger harddrive installed. The original harddrive size is around the 6GB depending on the model. Not much that can solve this problem I'm afraid (apart from running Norton Speed disk which sometimes helps). I have an imac 333mhz with a 40GB harddrive in it and it occasionally has troubles starting the harddive up. I just turn it out and then try again, as soon as it's started up properly, it works fine.
If its running OSX then this has to be on a partition within the first 8GB.
Try zapping the pram at startup with I think the keyboard command Apple+CTRL+P
A fresh install of the system would probably do the computer the most good and also because of the computers age it's possible that the internal battery is at the end of its life.