Stop: C000021a (Fatal System Error) 0x00000080.

I am a home user with a Demension 2300 desktop. I went to microsoft.com to download the latest security patch. Almost at the end of the download, I received a message that it could not continue. I exited, rebooted and get a blue screen with the above message. I cannot boot with Windows XP CD, or any other utility CD. I cannot even boot in safe mode. The same blue screen appears with the above message. Can anyone help or offer advice?

Thank you.