Apart from scratched or damaged discs, CD players can have difficulty playing music if the device is out of alignment. Typically, players that cannot recognise a CD or have recurring problems with skipping need some basic cleaning and maintenance. You can perform these steps yourself. If you're still having issues, you may need professional help.
Clean the laser. One of the most common causes of skipping is dust or dirt that has collected on the sensitive parts of the player. Buy a cleaning disc from any electronics or department store and use it in your machine. These discs have small brushes that clean the laser emitter.
Clean the mechanical arm. The laser is housed on an arm that moves while the CD is playing. Dust or debris can easily cause the arm to get stuck. Spraying compressed air into the CD slot can remove this dirt and allow the arm to move freely again.
Open the CD case. If neither compressed air nor a cleaning CD works, you'll likely have to realign the laser. Unplug the player and remove the screws on the outer case. Use a small screwdriver to take out each screw and put them in a safe place.
Remove the CD tray, the plastic piece that holds the CD and moves in and out of the player. The tray is often in the way of the lens and aligning mechanism, so you may have to remove it.
Locate the lens and motor. The laser lens is a clear, circular glass piece located on an arm. There should be a small motor there that moves the laser on the arm.
Lubricate the arm. Use a proper lubricant and apply it to the arm mechanism after making sure it's clean. You can use a silicon or Teflon lubricant, or any lubricant appropriate for electronics and small motors.
Close the case. Once you've lubricated the moving pieces, replace the tray and screw the cover back into place.
Not all CD players are created equal. Some will require more extensive repairs or have pieces that are harder to access. Read your user's manual thoroughly. More extensive repairs and adjustments probably will require a service manual.