2000 Pro reboots on first login.

The computer is started, Ctrl-Alt-Del is pressed to bring up the login screen, the password is entered and when you press the enter button or click on Ok the computer reboots. After the computer restarts the logon works.

This happens on Dell C600 laptops and Dell Optiflex desktops running Windows 2000 Pro that have been fully updated with Security Packs, Security Updates, and device drivers via Windows Update.