Lsass.exe error at boot up

>Hi my name is Oliver and I have a trouble with a notebook DELL Latitude C840 running on Windows 2000 Pro.

When it starts to boot I get the great message:”the security ID structure is invalid Error status 0x0000078″.

This message comes from the LSASS.EXE. I scanned the hardrive and there are no virus.

When I boot from the CD, I enter the password but it cannot recognize it.

I believe the LSASS.EXE is corrupted. Is anybody has a solution for a such bug?

Thanks,

Oliver