My advice would be to try a bootdisk along the lines of sbootmgr. (Google it to download it.)
I have a pesky PC that will only boot from certain CD's. Never took the time to figure out just why, I will most likely retire the PC since I only use it as a firewall. Anyway!
The bootdisk mentioned above will "force" the PC to boot from whatever media is attached to it. That's not the technical term for it, but you get the idea.
Oh yeah, you'll need a floppy drive for that to work.
"i would never use a firewall, even without a router protecting me. Firewalls are just wastes of memory."
name omitted to protect the innocent
the cake is a lie