Pop it open with a screw driver (as in, unscrew the screws) and get it down so that you can access the laser. Spray some isopropyl alcohol on a q-tip and clean the lens. Maybe take a dry q-tip and wipe off any excess alcohol. Reassemble.
I found some isopropyl alcohol in a 'CD Cleaning kit' (with some cloths and whatnot). You can probably get it a drug store or something.