Is your PS2 can't play all the games or only DVD9 games? Here is what you can do to know wether you have laser problem or modchip problem.

1. Put in an audio cd (pressed or cdr disc). If all of the songs can be played then your CD diode is ok.

2. Put in a DVD movie (pressed or DVDR). If the movie plays well then your DVD diode is ok.

Conclusion, your laser is still ok.

If both step 1 & step 2 or either steps fail then it is confirm that you laser is gone.

3. Both step 1 & step 2 are ok but still can't boot any PS2 games (you got Red Screen Of  Death), you might have a dead modchip or any of the modchip wires loose.