Well like you said you have never opened it before so i suggest you use this guide on how to open it first.
http://www.exploitstation.com/index.php?page=ps2repair
As you see on the third picture there is a lense in the middle. On each side of the lense you have these two metal sticks on which the lense moves up and down. You have to lubricate or put some greese on these two metal stick so that the lense can move. That did it for me hope it helps you. Ohh and by the way make sure you work on you'r ps2 plugged off! Best of luck