Fatal Error when booting up XP sp2

I’m having issues when trying to boot up an XP Pro machine. No updated have been added and no new devices have been attached. After the windows xp splash screen I’m receiving ” STOP: c000021a Fatal System Error. The windows logon process system process has terminated unexpectedly with a status of 0X00000502. This system has been shutdown”
I have looked all over the internet for 0X00000502 but have found nothing. I have ran chkdsk -r, last good known config, fixmbr, and fixboot. Nothing is working. I can however log in using safe mode.
Any ideas or suggestions would be great.

Thanks