Presumably you cannot boot in Safe Mode either.
If you cannot, then perhaps a repair of XP using the Recovery Console is
your best option.
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Reinstall Windows XP by starting your computer from the Windows XP CD
1.Insert the Windows XP CD into your computer's CD-ROM or DVD-ROM drive, and
then restart your computer.
2.When the "Press any key to boot from CD" message appears on the screen,
press a key to start your computer from the Windows XP CD.
Note Your computer must be configured to start from the CD-ROM or DVD-ROM
drive. If necessary ypu can set the boot order in your BIOS using Setup.
3.You will receive the following message on the Welcome to Setup screen that
appears:
This portion of the Setup program prepares Microsoft Windows XP to run on
your computer:
To setup Windows XP now, press ENTER.
To repair a Windows XP installation using Recovery Console, press R.
To quit Setup without installing Windows XP, press F3. Press ENTER to set up
Windows XP.
4.On the Windows XP Licensing Agreement screen, press F8 to agree to the
license agreement.
5.Make sure that your current installation of Windows XP is selected in the
box, and then press R to repair Windows XP.
6.Follow the instructions that appear on the screen to reinstall Windows XP.
After you repair Windows XP, you may have to reactivate your copy of Windows
XP.
After you perform an in-place upgrade or repair installation, you must
reinstall all updates to Windows.
To reinstall Windows updates, visit the following Microsoft Web site:
http://windowsupdate.microsoft.com