Your Windows 2000 screen saver may not run if:
1. The screen saver is configured to start after 2 or more minutes of inactivity.
2. The Press CTRL+ALT+DELETE to logon, has been disabled.
NOTE: It definetly won't run if you Lock Computer and both 1 and 2 are true.
NOTE: Windows 2000 Pro, in a workgroup, disables the CAD dialog, by default.
To require the CAD dialog, use Regedt32 to navigate to:
On the Edit menu, Add Value name DisableCAD, as a type REG_DWORD. A data value of 0 requires the CAD. A data value of 1 disables it.