I've sometimes noticed that they connections that the crystals slide into stop making contact. Try to pry them in a little to make a tighter connection to the crystals. Also, do you have multiple crystals of the same label? The reason I ask is because I have a lot of crystals, and some of the ones labeled the same still will not work together, i.e. some of my label 3 crystals will only work with certain other label 3's.

Does the power light turn on your remote when you turn it on? If you touch the remote antenna to the car, will it work then? If it's not those, then it's not a power problem. When did it last work and what changed since then? These are the questions you need to ask yourself. Isolate all the variables you can and test them. It helps us out a lot too if you can tell us what you have tried and give more details about the problem.