If there are dust particles on the Lens of CD or DVD drives and writers then they won't read Cd's or Dvd's. We can clean the Lens with one or two water drops like this.
First unscrew the Drive from the computer. Take it out from the computer. You will observe 4 screws on one side of the CD Drive. Unscrew those four screws. Then open the iron sheet cover from the drive. Then you will observe like this.
In the above figure you will observe that Door of the CD Drive is locked and front plastic cover is also locked. The screw driver is showing door locking point in the above figure. You can clearly observe it from the figure below.
With the help of screw driver move the locking point to the left. Then door lock will be released. Now you can release the front plastic cover by pressing two small plastic locks on left and right sides of the drive. Now remove the second iron sheet cover also. Then you will observe the CD LENS as shown below.
The CD Lens is in the circled mark(The Door of the CD drive covers the Lens). Now with your finger put one drop of water on the Lens then clean the lens with a clean paper until it dries. Now cleaning Lens is completed. Now arrange the CD drive as usual then Fit it to the computer as usual.
NOTE: After reading this article first observe the cleaning procedure when any experienced person is doing the Lens cleaning. You can easily understand how he is doing the Lens cleaning. After you got confidence then you can also do the same as explained above.