The PSTwo has two door sensors. Nothing will spin if it thinks the door is open. The first and least likely to fail is a little black nub right above the power switch. It must be pushed down. The second is way at the back, to the back left of the laser assembly, and is a white or brown plastic box with a tiny plastic nub sticking up. It needs to be down as well.
Easiest way to test is to remove the lid altogether, and manually press down both sensors, because you can access them both easily. Have a disc in, turn it on, and press down both sensors. If it works, disable one or both of the sensors, and you should be playing in no time.