If that did not work, I would not know how you would be able to fix it without a XP install disk. I cannot guarantee it but if you reboot, I think you would be able to access safe mode by tapping F8 at boot. This would load XP with a minimum or drivers. Then you could use System Restore to take your computer back to a date when it was working. This is if you have System Restore enabled
Do you have another XP computer that is working? Do the steps here to create a bootable disk that will let you do a System Restore on an unbootable XP. You can use isoburner or Imgburn to burn the iso if you do not have software that can burn an image. You can also use this disk to back up data to an external USB drive but you first have to attach the USB drive to the computer before you boot the disk.
If you do not have another XP computer:
For XP I recommend you download Puppy linux 5.2.8. You can burn the iso file to a disk using Windows 7 by right clicking and selecting Burn Image or use a image burning program like isoburner or Imgburn. If you decide to use Imgburn, opt out of any optional programs. Burn the iso at 4X if possible.
After burning the iso, boot the Puppy disk. Nothing is written to the hard drive. It runs from RAM and the CD. Using Puppy you can backup the data to an external drive.
If you decide to use Puppy post back and I will give more details. The other option of getting your data is to remove the hard drive and attach to another computer via an adapter, external enclosure, or internally.