Ian

I would recommend checking your CD for cleanliness, scratches or dust on the CD will cause problems. Next you could try to blow any dust out of the optical drive with a can of compressed air. Then if that doesn't help I would recommend looking at the troubleshooting page or if necessary you can replace the optical drive on the computer, there is also a guide for that as well.

For a cracked screen, unless you are just willing to deal with the crack, there is really no way to fix it without replacing it. See the troubleshooting guide for more information regarding various screen issues, as well as a link to the replacement guide.