New imac user needs help

Hi,

I was given an Imac from a friend who no longer used it, however it
has a fault. As soon as you turn it on a flashing question mark
appears, after reading several comments on these newsgroups I came to
the conclusion I would need to purchase a startup disc. The first set
of discs I ordered were specificly for the Imac, the OS 8.6 and
restart disc were included, however both failed to boot the machine
when holding the C key. I then came to the conclusion that I would
need the full retail version of mac os rather than the imac specific
version, so I ordered OS 9, it arrived today and guess what it still
wont boot the machine!!

What am I doing wrong? The machine starts normally and you can hear
the HD and Cd both making the usual noises. Ive tried resetting the
ROM, but this had no effect.

Im quite familiar with PC's and when taking the IMAC apart I found
nothing unusual.

Any help would be greatly appreciated.

thanks for you time