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Sometimes it's not the lens (although that's a good place to start). Capacitors in the power supply can also cause that problem. If you open the case and identify the power supply you can check for bulging caps or the tell tale smell. Successfully fixed this problem on a Tascam recording cd deck by replacing the caps.
I've cleaned the lens roughly with a q tip on a pencil in a computer drive but eventually replaced it as they're easy to do and cheap. If you open up the case you can eventually get to the lens to clean it but it's a pain.
My cd deck (20ish yr old wharfedale 901) has begun occasionally not recognising CDs. Can the lenses on these be cleaned at all like tape decks could?