Hello you experts out there i am in dying need of some information on whats happening to a friend of mine computer. the problem is everyime i boot up it goes to one point and it shut down saying stop: C000021a( fatal system error) the windows logon process system process terminated unexpectedly with a status of 0 x 00000000 ( 0 x 00000000 o x 00000000) the system has been shut down. Thats the message thats been coming up guys. any advise or suggestion will be thankful for. thanks in advance.

Can you load "Last Known Good Configuration?" Life is more painless for those who are brainless.

Is the fatal error represented in a blue screen of death? possible RAM malfunction?

Try booting into safe mode Then check the Service for the Net Logon and make sure it is set to automatically start and is using the system account. Also check to make sure the Workstation service is set the same way. If you can get into safe mode and it still doesn't work try replacing lsass.exe with a known good copy from another 2000 computer