Here's a really good walkthrough for calibrating the laser.

http://arstechnica.com/articles/paedia/hardware/ps2.ars

One thing the PS2 is notorious for is DRE's and weak lasers. Follow the guide right and you should notice a big difference. I would advise cleaning the laser with a little alchohol while your in there. You can try cleaning the lens 1st and see if that helps (fixes a lot of issues expecially with CDs not reading). If not, it's time to calibrate.
**Note, doing this will forever void your warrenty with sony! Notice the nice little label on the back reveal the words VOID as soon as you pull it off. Be careful and follow the guide explicitly and you should be fine, but don't cry to me if you break something. I'm not responsible for being clumsy**

Good Luck :thumbsup: