Also be sure that if you have 2 cd-rom drives the correct one is selected in the bios, or just put the cd in the other one and see if it boots. Keep in mind it won't boot by itself, you do have to hit a key like someone mentioned, this may not be displayed because of the splash screens many manufacturers install usually it says something like "hit escape to show boot process" so i'd make sure you do that too. Other than that just make sure its not a copied cd, and if it is go buy a retail version.
