install linux on imac G5

I have iMac G5 (Tiger) and like to install Linux. I tried bootable USB and DVD(yes I pressed C and optipn key and option key with apple key together ), but failed to be recognized by the mac, simply don't see them. I changed hard disk and installed new hard disk with Linux(Ubuntu) and another hard disk with Windows 10 both failed to be discovered by machine and simply says no OS. only want mac, mac , mac nothing else is acceptable. Could any body help with solution how to make this machine to either see bootable USB/DVD with Linux ISO or accept complete new hard disk with Linux.

Thanks