going Start > Run, then typing in ( or copy and paste this )
Note space between sfc and /.
Failing that, why not try a repair of XP as follows:-
Configure your computer to start from the CD-ROM drive.
Insert WinXP CD, restart computer.
When the Press any key to boot from CD message is displayed on your screen, press a key to start your computer from the Windows XP CD.
Press ENTER when you see the message To setup Windows XP now, and then press ENTER displayed on the Welcome to Setup screen. Do not choose the option to press R to use the Recovery Console at this time.
In the Windows XP Licensing Agreement, press F8 to agree to the license agreement. Make sure that your current installation of Windows XP is selected in the box, and then press R to repair Windows XP.
Follow the instructions on the screen to complete Setup