Hey mate, first off. I know you have tried the brake release, but have you tired both (there are two that need to be pushed down to allow the disk spin). There is one near the power switch. The other one is towards the back, left of the laser assembly. This photo shows there location;
http://www.richspsxparts.com/howto/lidclosed.jpg
If that isn't it, it could be a faulty laser or motor problem. It could be a problem with its wiring (the motors ribbon cable sometimes is the problem, so inspect that) or it has simply died. If not a motor problem. It could also be that the laser can't read the disk/detect there is one, the motor won't spool up/spin. The laser is what tells the motor to pin, go a set speed etc.
If you want to try a new laser etc, you will need your PS2's model number. This guide should help you out, to insure you order the correct components;
http://www.ebay.com.au/gds/How-To-Determine-Your-PS2-Playstation-2-Version-/10000000000069070/g.html
Hope this gives you something to go on/help you.