m-eken

This way is faster than format or re-install to repair Windows XP.
Insert the XP cd to the cdrom, and restart the pc for boot from Windows XP cd.
Press [R] key when you see “Press ‘R’ for repair” words bottom the window. You will get the Dos screen. Within Dos screen type the following:

c:\windows>cd system32
c:\windows\system32>cd config
c:\windows\system32\config>ren software software.bak
c:\windows\system32\config>ren system system.bak
c:\windows\system32\config>cd c:\windows\repair
c:\windows\repair>copy software c:\windows\system32\config
c:\windows\repair>copy system c:\windows\system32\config
c:\windows> exit

Some installed programs may be do not run. May be require re-install.
Users will be deleted.
You would not lost any data. If lost this is your success(!)