Usually what happens is that it tries to do a basic read from the laser assembly. If there is no read, it stops. '
The only things you can do at home are the basics. Check to see if the ribbon cables are properly seated. You can remove the circuit boards, and look for any cold solder connections that would be visible. These boards are in multi-layers, therefore not everything is able to be checked visually.
As for actual diagnostics, you will need the service manual, training, and proper tools to continue. CD, and DVD players are very sophisticated, even though they may look visually simple.