Maybe time to eliminate some variables....
First--as already mentioned--make sure the Windows CD will boot up in another computer.
Next, try some other bootable CD in your computer. Since you may be needing a utility disk to delete the partitions, I would go ahead and get something like GParted Live CD. You can download the .iso here
. The .iso file is used to burn a CD, which you can then boot. Another option is just about any "LiveCD" version of Linux. If nothing else, you can get one from a Linux magazine.
Before or after the above, you can also try cleaning the CD drive. There are cleaning disks available, but you can also do it by hand. Simply open the drive and carefully
brush away any dust, and wipe off the laser lens with a soft cloth.