In about this mac, system profiler, Serial ATA. The first box is the path with the hard drive below it. Then the path with the optical just below that. The optical drive should say the same as if does in disk utilities. When clicked on you get more info on it. If you put in a cd and then open system profiler. It should now show as on. If your install disk reads in the external optical drive. It should also read in the internal one. If you can hook up an external optical drive with no problem, it may be that the one you got from sears is defective. One of the things that make an optical drive eject a disk without mounting it is, it cannot read the disk. This could be a software problem, as to the driver. Or the laser in the drive is weak.