Why won't my screen turn on but my cd drive will?

Sorry your having trouble. Here's what I'd do.

1. Plug in an external monitor. ReStart computer. If you see something on external then you have an issue with your macbook internal display. If nothing comes up on external then ...

2. Do a PRAM reset by holding down (Command+Shift+P+R) and keep holding them down while you press the power button. Hold down until you here the second startup chime then release.

3. Perform an SMC reset. Just google SMC reset with the model number of your Macbook and it's pretty straight forward

4. Hold down the "option" key when starting up. If you see a recovery screen then you are a little closer.

I hope this helps. Not knowing exactly what is happening is difficult to diagnose but this should get you started.