|I know from experience that you can install Windows by booting from the CD and running Setup, and Setup will reboot the computer several times and complete successfully, even if the Boot Order or similar settings are wrong. |
You don't get the "operating system not found" or similar message until you boot after Setup is finished
Check the Boot Order or similar settings in your bios Setup.
They should be
removable drive, or floppy drive
CD-rom or similar
network boot or similar
with some bioses, if removable drive (or USB drive) or similar is first or before hard drive in that list, the bios may attempt to boot from a USB external drive or a USB flash drive. A USB flash drive is never bootable unless you follow a procedure to make it bootable - if it's not bootable you will get the "operating system not found" or similar message and the bios will not attempt to boot from anything else in the Boot Order or similar list.
Try unplugging any USB flash drives before booting.