The Windows XP Professional startup process closely resembles that of Microsoft Windows NT version 4.0, Microsoft Windows 2000, and Microsoft Windows Server™ 2003, but it significantly differs from Microsoft MS-DOS, Microsoft Windows 95, Microsoft Windows 98, and Microsoft Windows Millennium Edition (Windows Me).
The POST is responsible for the following system and diagnostic functions: After the motherboard POST completes, add-on adapters that have their own firmware (for example, video and hard drive controllers) carry out internal diagnostic tests.
To obtain a list of environment variables useful for troubleshooting, type set at the command line.
For more information about environment variables, see “To add or change the values of environment variables” in Windows XP Professional Help and Support Center.
If the condition is serious enough, you might need to reinstall Windows XP Professional or restore files from backup media.
In x86-based systems, startup failures that occur before the operating system loader (Ntldr) starts could indicate missing or deleted files, or it could indicate damage to the hard disk master boot record (MBR), partition table, or boot sector.