Could be a faulty drive. Try inserting a bootable CD, such as the Windows disc in and booting from it. Remember to make sure that the PC is set to boot from a CD in the BIOS first. If the CD boots then it is most likely to be something in Windows that is stopping discs being read. If it doesn't boot and goes straight into Windows, then try a bootable floppy and start the machine with CD-ROM support. Put a data CD in and type in D:\ (or whatever letter your CD drive is) and then type in DIR. If a list of files and folders come up that are on the disc then the drive is working. If it comes up with an error, then the drive is faulty and you should get a replacement.