Check in device manager (do a search for device manager) open the tree that
lists your DVD/CD drive and see if their is a yellow caution sign there.
Highlight it and see if any information (error code is given).
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If the DVD/CD is not available in Vista but is physically installed,
you can look at this Microsoft post. It's written for XP but applies to
Vista: http://support.microsoft.com/kb/314060