No bootable device / iMac 20-inch late 2006
My old iMac (late 2006) has lost its boot sector. Message is when it is turned on "No bootable device -- insert boot disk and press any key". I do not have a boot disk, at least not one that I can find.
I do not remember what I may have done to get it in this state, probably in 2012/13. I think that I may have tried to set it up as a dual-boot device to run either the Apple or Windows operating systems. The computer has been put away in storage since then but now I would like to get it working if that is possible.
Is there anyone here who can suggest a reasonably straightforward method for me to reactivate this iMac to get it booting up and working?
iMac