There are many problems people report with very CD and DVD drives.
In order to help you better we need some more information. You are using Microsoft Windows Vista. Is this on a desktop? Is this on a laptop? Have you made any recent changes to your software or hardware? When did this start to happen?
Here is a very simple test. Set your computer up in the BIOS to boot from the CD/DVD drive. Stick in your OS install disk, or any other bookable disk you have around, such as say Linux distribution. See the computer will boot up to the first screen of the disk. But don't let it go any further. If you get that far then that would indicate that the disk drive is basically usable and your settings in the BIOS are correct.
So if that's the case, and it does try to boot the CD or DVD and it looks like it's going to work, we would could figure that something is wrong with the drivers inside of the operating system.
Otherwise, if the BIOS cannot create the optical disk drive, or does not predict reliably, we would conclude that the optical drive is at the end of its life.