If Windows won’t start, use the DOS-like Recovery Console to make repairs.
The Recovery Console is one of the last-ditch tools you can use if your Windows installation doesn’t start up at all. Before you resort to the Recovery Console, if Windows starts up make sure you’ve already tried System Restore (especially if you’ve recently changed your hardware).
If it won’t start, try running the Windows XP Setup Wizard from the installation CD and choosing its Repair option, or try starting Windows in Safe Mode.
If none of these easier paths works, you’re stuck using the DOS-like Recovery Console to figure out what’s wrong with Windows, your system or boot partition, or your disk’s master boot record (MBR). You can use its DOS-like commands to look at the files and folders that make up Windows, and possibly to repair them. You can also repair the master boot record and boot sector.