1. Check the short-circuit switch for the laser. You might switched it when replaced the laser unit and forgot to switch it back.
2. Check the ribbon of the spindle motor, you might have forgot to connect it.
3. Can you load cds in the unit? When you push a cd in does it accept it? If no, then probably the fuse of all the motors is blown and should be replaced. This is the part: http://www.artaudioparts.com/product/aek7009http://www.artaudioparts.com