Oh dear. Did this suddenly happen? There are so many things that could cause this from the effects of certain viruses to corrupted files. If you think there is any chance of the former then you really should reformat and hope that this allows you to reload windows (there is a chance that a key file on your hard disk has been corrupted in which case it is rather more complicated). However let's look on the bright side and try a couple of things first before doing something as dramatic as a reformat - and loosing all your data. It's odd and worrying that you can't boot from the windows CD, however here is a chance that your PATH is incorrect. To test this enter the following two commands, pressing the Enter key afer each:
CD\WINDOWS then
WIN
If that gets the machine booted up and running then the cause of the problem is a bad PATH command in the autoexec.bat file. Use Start - Run -
MSCONFIG and go to the AUTOEXEC.BAT tab. Look for any lines with the word PATH (or SET PATH) at the beginning and click on the checkmarks to clear
them. That will correct the startup problem. If this doesn't work then there are a few more things to try.