|"It isnt an issue of order of boot"|
"I also tried to boot into CD-ROM, USB stick and even the hardy old floppy drive"
The computer can only boot in the order it's configured for. If the order is correct (floppy / CD / HDD), the system will 1st attempt to boot from a floppy. If no floppy is detected, it will try the CD drive. If no bootable CD is detected, it will try the HDD. If no HDD is detected or the HDD is defective or there's no OS on the HDD, you'll get the "operating system not found". Also, if you leave a non-bootable disc in the floppy drive, the system will stop the boot process & display "operating system not found".
Please answer my other question - is the HDD detected in the BIOS? If it's not being detected, there's your problem.