Test, if the laser is searching for a disc.
1. Look, if the lens is moving.
2. DON'T LOOK AT THE LASER-BEAM DIRECTLY!!!
You can use a CD as 'mirror' to look at the laser,...
It'll 'break' the laser-beam so it isn't dangerous for your eyes anymore.
...or simply put a piece of paper over the laser-lens and look, if you can see a red point 'glowing'.
If it isn't even 'on' in the beginning when you start your PS2, it's either a sensor or a defect laser.
I suppose it is a sensor, but I'm not sure... (I can't look at it on my own, so...)
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux