Is the disk visible when you open the tray?
If not, it may have ended up between the DVD-ROM and the chassis. You should be able to remove the DVD-ROM drive temporarily to pull out the disk. Usually there is one screw on the bottom of the unit which holds the DVD drive in place. If you're not sure which screw it is, just track back a bit more than a DVD width from the edge where the drive is located and look for a screw in that area. Turn the laptop off before you remove the drive, and use a pin or a straightened paper clip in the small hole in the side of the DVD rom plate to open the mechanism and gently pull it out from the laptop. This should pull the drive out and expose the disk.