You can back out SPs using Add and Remove Programs in the
Control Panel. However, if you have SP4, Add and Remove
Program does not seemed to work under SP4. If you have
windows 2000 professional, use the installation CD to do
the emergency repair. After the repair, you can then use
Add and Remove Programs to remove SP4. If you have
advanced server, try the emergency repair. If successful,
back out SP4 immediately - do not hesitate. If not
successful, re-install after reformat. One word of
warning - make sure you have backed up of all key data
including all the known device drivers before attempting
the repair. You may need then if you re-instal.