Win xp lsass.exe system error

Am running Win xp on my laptop & running through a problem. Win Xp boots up & displays dilog box alog with a login screen, the lsass.exe system error dialog box says The specified domain did not exist. ignoring the error if i try to login to domain the system hangs.
When i close the error dialog box system restarts.

this repeats am not able to log into my system even in safe mode.

whatz causing this behaviour. even if it is a virus the least i need is log into system.

any solutions ?

thanks in advance ..