Why is my discman skipping on some cds?

After some failed attemps, I've finally dissasembled the Diskman.

Two days ago, I bought a Dream Theater cd "Falling Into Infinity", alright, when I put on Track 7 "Lines in the Sand" or at the end of track 6 "!&&*'s Kitchen" it sorta stops and the motor spins faster and the laser cannot find the track. But when I tested the cd on my computer or my dvd player, both tracks run smoothly. What it would be?