did you replace the laser with the same model?
I only replaced the laser, how do I know if it's out of alignment ? It seemed pretty simple to replace 4 screws and out it came then reverse, I have the drive taken apart and when I put a blu ray disc I can see the blu light flicker and skip
How tight your screws are, how much torque you applied, and even which order you take out and put the screws back in could affect it.
That said, it isn't a common problem. Did you oil up the tracks and gears as you inserted the laser head?
it is not your playstation... after the 4.31 update many pepople including me can not play some disk based games. dvd's,music and online games work fine. sometime's if you leave your playstaion on for about ten min. with the game in you can eject,insert and it will reconize it. software problems suck...