If you disconnect the CD drive and it still didn't boot, then the problem isn't the CD drive.
At what point does the booting process stop? Does the system get past the POST? Does Windows begin to load? Are there any error messages? You need to be more specific. Remember, we can't see what it's doing so you have to provide as much detail as possible, even if those details seem irrelevant.
Best guess right now, could be the hard drive or the memory or even a number of other things. Can't say without more info.