By Jim Boyce, TechRepublic
Wednesday, April 26 2006 09:56 AM
URL: http://www.zdnetasia.com/techguide/disasterrecovery/0,39044895,39353965,00.htm

The Windows 2000 registry comprises a handful of hive files located in the %systemroot%\System32\Config folder. When Windows 2000 starts, it builds the registry from these files. One of the registry files is the SYSTEM hive, and a corrupted or fragmented SYSTEM hive can prevent the system from booting.

When the system first boots, it's limited to 16 MB of memory. A highly fragmented SYSTEM hive can cause the maximum amount of memory to be exceeded, thereby preventing the system from booting. Defragmenting the file can be a quick fix. You can defragment the system drive inside of Windows 2000, which is a good reason to do it on a regular basis; but if your system has sufficient contiguous free space, you can overcome the problem through the Recovery Console (RC).

1. Boot the system to the RC and then use the CD command to change to the %systemroot%\System32\Config folder.
2. Rename the existing SYSTEM file to SYSTEM.OLD.
3. Use the command COPY SYSTEM.OLD SYSTEM to create a new, unfragmented copy of the SYSTEM hive.
4. Exit the RC to restart the system.

If creating an unfragmented copy of the SYSTEM hive doesn't fix the problem, it’s possible that the SYSTEM hive file is corrupted. If you have a good version backed up in the %systemroot%\Repair or %systemroot%\Repair\Regback folder, boot to the RC again and then copy the backup SYSTEM hive file to the %systemroot%\System32\Config folder.

Note: As always, we'll remind you that editing the registry can be risky, so be sure you have a verified backup before making any changes.