NT4 SP6A Rebooting continuously

Had an NT4 System running SP6a working fine. I needed to reapply the service pack again, as i had RAS issues and Microsoft Technet article reccomended it. Now the system gets to the point where the gui is loading, background comes up and the system reboots. This works in both VGA mode as well as normal mode. Any suggestions before I have to wipe and start again? My data is still there and the drive is accessible from another NT installation.

Thanks for an help