Firstly - Dont even think about cd cleaning discs - not only are they useless, but the brushes on them risk knocking the lens out of alignment or damaging it, though luckily I havent had that myself.
Instead, open the unit (unplug first).
You may have to apply power, press eject, then unplug again to get access, or you may have to gently slide the sled (which the pickup is mounted on) into a more accessible position.
Apply pure alcohol onto a Qtip (get both from the chemists - or tape head cleaner solution will do, as this is usually alchol based).
Then *gently* wipe it across the lens and dry excess. You will notice the lens is spring-mounted. do not apply too much pressure or you will damage the assembly.
This works on DVD players too if they act up.
That method has worked for me on at least 50 occasions over the years.
good luck!