AMD 64 PC reboots after Windows Update

I have an AMD 64 system, Giga-byte K8VM800M motherboard with a 40GB Western Digital Caviar IDE HDD.

All goes well until I apply Windows Updates to the PC. After that, the PC will cycle through the splash screen fine but will reboot after that. Repetitive cyle.

I have updated the BIOS and have changed jumpers on the drive from Master to Cable Select, no change.

I am using an OEM copy of Windows XP.

Anyone have ideas? What update could be doing this?