Try booting the computer with a bootable disk. This can be a Window install disk, a live Linux cd or something like the Ultimate Boot CD. http://www.ultimatebootcd.com/
You'd have to make a copy of the UBCD in another computer of course.
The boot order of you computer has to be set to look for the optical disk drive first, rather than the hard drive. So you should look in the bios of the computer to set boot order. It is a good idea to look in there anyway, to see if the optical drive shows up there.
The whole purpose of trying to boot with a disk in the optical drive is to see if it is working outside of the Windows operating system. If it will boot up, then there is no mechanical problem, or connection problem with the drive. This narrows down the possibilities to software issues.