You need to reinstall Windows from scratch. You might find this useful from PCSupport.
http://pcsupport.about.com/od/operatingsystems/ss/installxpnew1_6.htm
Turn on your computer, and when it gives you the choice to go to the BIOS, take that choice.
Then look at your Boot order. You want the computer to boot to the CD. Set the choice so that going to the CD drive is the first choice when you boot.
Insert your Windows Disc into the CD Drive, and reboot.
The Windows disk will boot and allow you to go to a blue screen that will give you the choices to setup a new install, create a partition in unpartitioned space, or Delted the selected partition.
Select "Delete the Selected Partition" or words to that effect.
and the Windows disk will remove that partition, then do so again and again until ALL partitions are deleted.
Then select, "Create a partition in the unpartitioned Space"
This take only a brief amount of time, then select the choice to install Windows. If you do not get that option, reboot the CD and select "Install Windows XP" which will begin by formatting the hard drive, then installing Windows.
The CD will now begin the formatting and installation of Windows showing you a yellow bar of progress. It wil take as little as 30 minutes or as long as 90 minutes depending upon the size of the hard drive you are formatting.
From there, it should be easier for you.
Point 1, you must boot to the Windows CD
Point 2. you must delete ALL the partitions.
Point 3, you must then create ONE new partition.
Point 4. you must format that partition which will be automatic but take a long time. You will end up with one large partition that encompasses the entire drive... give or take a few mb's.
Then you find that you are installing Windows, and it will work smoothly, yet take some more time.
Finally you have a basic install of Windows, which now needs a chipset, then Video graphics installed, then ethernet, audio, and all the other drivers.
I hope this was more helpful without taking up too much space.