Check out this thread about a similar issue:http://www.tomshardware.co.uk/forum/77667-20-laptop-drive-working
The solution there was to clean the laser of the CD/DVD player.
A couple further questions could help to solve the problem:
- is this a new computer?
- was this computer's operating system recently reinstalled? Any other major software change?
- have the cd/dvd player worked previously?
- does your cd or dvd disk that you're trying to use work in another computer's player?