how to repair imac boot

Hi,
I have the following problem:
I plugged a ufs hard disk (an old Quantum Fireball 4.1 gb with mac os 8.1 from an iMac G3) containing some important data on a windows 7 pc in order to take a backup of the disk ( i know now that was a stupid thing to do). Windows messed up the disk writing the MBR and now I can’t boot the Mac. I tried to boot using the software restore cdrom in order to try and repair somehow the boot record but the system denies booting from cd. I also tried to use an external usb cdrom (I am not sure if the cdrom is working) with no luck.
I would be really grateful if you could help me with the above issue.
Thank you in advance.

any help please?

I believe you're out of luck. If Windows 7 overwrote or initiated the drive, that means the partition info along with the MBR was destroyed. The data may still be there but since that drive and version of OS is so old, I don't know of any way to recover it with modern software.

You may be able to search and find software or a method that can recover the data. But keep in mind that OS 8.1 is ancient.

Well, thank you for your reply. I have already managed to backup/copy the data but I have to bring the system back to life. Any idea how can I boot the machine from cdrom and fix the boot record?