Microsoft Knowledge Base Article 315396 contains the following summary:

This article describes general procedures that you can use to troubleshoot startup problems in Windows 2000.

A successful Windows 2000 startup consists of the following four phases:

Initial phase
Boot loader phase
Kernel phase
Logon phase

If a problem occurs during one of these phases, Windows may not start correctly and you may experience one of the following issues:

The computer stops responding (hangs).
You receive an error message.

If a startup problem occurs after you click Microsoft Windows 2000 on either the boot loader menu or when you receive the "Please select the operating system to start" message, files that are required by the operating system may be missing or damaged. Windows 2000 provides a variety of options that you can use to troubleshoot this issue, including safe mode, Recovery Console, and an Emergency Repair disk.