PS2 DVD ERROR

[takarot]

hi!
I've recently bought a PS2 and have been playing until the dvds won't read properly anymore. The cd games work fine but the DVD games either do not work or load VERY slowly. Is this common?? What is wrong with it, could it be a laser calibration error? (The PS2 has not been opened before and has been sitting in area free of damage). Please help. I miss it a lot.