This is a tutorial for reparing a PS2 when it will not detect the game disk warning! Doing theis voids your warenty! Do so at your own risk or if you dont want to wait one month to play it! Now that I warned you heres the tutorial and do not use alcohol! It can short out the wiring if you use to much! meaning it can break the PS2.
First, turn the PS2 upside down, see the pads and 6 or 4 plastic squares? pry them off with a flat head screwdriver, they should come off easily. Next get a pice of paper, make a diagram of the PS2's bottom and punch a hole where each screw is, keep it if you want becaus this problem is most likely going to hapen again, unscrew all of the screws and put them in their respective holes on the piece of paper becaus they are different leingths, now you can flip it back over make shure the botom doesnt fall off! Now carfuly remove the top, it is veary important that you start opening it from the back top corner closest to the power button, whene you see a white ribon take off the sticker that is on it but keep the sticker, now extremly carfuly lay down the top cover if that ribon will not go any farthur stop there, now you need to detach the reset/eject buttons from the top cover, gentaly pull them to the back wall of the cover and towards the farthest wall on the cover and towards you at the same time they should come out but you might have some trouble still, make shure you dont break that ribon, see why now? Now after you do that move the cover out of the way, get a small screwdriver and unscrew the panel that covers the CD drive keep the screws in a safe place, like in one of the screw caps, now gentaly clean the laser lense of with a Q-tip close it back up and it should work, also if you see anyother part with dust on it gentaly blow it off.
P.S. the CD drive might give you some trouble taking it off after unscrewing it, it is stuck on with a weak magnet, just pull a bit harder.
P.S.S. dont forget to put the reset/eject buttons back in place
e-mail me for a tutorial with only pictures and some instructions but it'll be a few days before I get back to you.