The only thing left to try is a bootable disk, like an operating system disk, or something like the Ultimate boot disk. You can download the image of the Ultimate boot disk and burn to a blank cd on another computer.
Insert it into the drive, then start the computer. You might have to look in the bios of the computer and make sure that the boot order is set to look for the optical drive before looking for an operating system on the hard drive. The computer should then try to boot from the disk in the optical drive. If it cannot, then your optical drive may be dead.
The reason to check it this way is that this method will bypass any problems that might exist in the operating system. This will test the optical drive directly.