My Power Mac G6 will not boot up, and I believe that I need to reinstall Mac OS X

So, on boot-up my Power Mac G6 gets stuck on the gray screen with only the folder flashing between the old macintosh logo and a question mark. From previous experience on older Mac computers, this meant that it was unable to see at least some of the files of the operating system, and I had to reinstall/repair the operating system-but that was when I had access to an installation cd. For this machine, however, all I have are the original warranty agreement, and "upgrade coupons." Is there a way I can download a repair iso and rip that onto a cd? Or do anything to try and fix it?

Thank you for your time