[Diesel]

Theres a guide on the internet that you can use, and it has something to do with a small cog which needs spinning to a certain extent, the cog sets how close the laser is to the Disc, hence why some games work and others don't. When I had hassle with my PS2 though, I just opened it and cleaned the laser with a cotton bud. Be careful when opening it though, theres a silver strip that is attached to the power and reset buttons, if this comes out, it is a real pain to get back in.