How to clean the lens on your CD burner:

http://www.howtodothings.com/computers/a3631-how-to-clean-a-cd-rom-drive.html

Inexpensive cleaning kits are generally available in the blank media section of most department stores. They contain a cleaning disk with tiny brushes mounted face-up and diametrically opposed and a small squeeze bottle of cleaning solution. You apply the solution the the brushes and spin up the disk for a few seconds to clean the laser lens. Normally, it's an indication that the lens is failing but it may prolong the life of the laser for a while.

Joe, HTH.