Unable to boot from CD

I have a Dell Latitude C610 which refuses to boot from CD. I have set the BIOS to boot from CD first, but it insists on booting from hard disk. I have changed the CD drive, but to no avail. When I put a different hard disk in the machine it happily boots from CD. When I try my hard disk in a different machine it again will not boot from CD.

Can anyone help please?