hay friends i am having a serious problem with windows 2000 server. when booting up it shows the following message

"lsass.exe-System Error: Security Accounts Manager initialization failed because of the following error: Directory Service cannot start. Error Status: 0xc00002e1. Please click OK to shutdown this system and reboot into Directory Services Restore Mode, check the event log for more detailed information."


and the system restarts.this is the back up server of the network and all clients are connected to this machine.
plz help me