It's not a lens, it's a laser diode. When the cover is opened the PS2 has a high hazard category because of the potential damage to your eyesight from an active laser.

If the unit is damaged have it repaired by someone who knows what they're doing. Otherwise enter the browser and wait for it to offer the game cd as a browseable option, select it and you should be good to go.

Is this for one cd only or all of them? Check the cd is clean and scratch free. It could be the disk is so damaged the PS2 can't read the index track.