Heidi, see if this helps
http://kadaitcha.cx/stop_err.html#0xC000021A



"Heidi" <Heidi@discussions.microsoft.com> wrote in message
news:23799BE2-61A8-4B30-9758-DC5EF150C700@microsoft.com...
> When I turn my computer on, I get a winlogon.exe error message. Then when
> I
> turn off the computer, it automatically restarts, and I have to shut down
> twice to get it to turn off.
>
> I disabled "automatically restart" so that I could see what error message
> I
> receive. I now get "Fatal System Error Stop c000021a".
>
> I'm not sure what to do now. Any help would be appreciated.