Remove your battery and attach the charger to the computer. Try to power on. Does it turn on then? Check if your backlight went out. You can do this by shining a flashlight through the Apple logo on the lid.
Hey Scott and sorry to hear about your d-pad. In the teardown I left that d-pad ring in place since the cleaning I needed to do was mostly underneath it.
Looking back at the picture, it does appear that there are 4 snap-like pieces, in diagonal directions, that hold the ring to the rest of the plastic. Are those what you meant that broke during your take apart?