What rickair said.

I've had that exact problem before. Make sure all the cables are plugged in.

Note: unplug the power cord, and then touch a metal object (the tower of your desktop should work well) to ground yourself, and then begin taking a look.

You'll have a power cord to the CD/DVD drive (looks like a large version of a USB connection to your iPhone), and a cord that connects it to your mother board (long and skinny). If both of those are plugged in there are a few other more detailed trouble shooting tips out there as well.

Good luck!!