HOW TO: Recover from Registry Corruption
One of the most frustrating experiences working with computers is when they won’t start. This 
frustration is usually compounded by cryptic error messages that don’t provide you with enough information to determine what’s wrong, let alone fix the problem. An advanced user might recognize that the files the messages refer to are registry hives, binary files that contain the Windows registry.
The first one is the Software hive, which contains the HKLM\SOFTWARE portion of the registry tree, while the second one is the System hive, which maps to HKLM\SYSTEM. The messages indicate that a portion of your registry has somehow been lost or corrupted, and as a result, Windows can’t start.
The simplest way to resolve this situation is to restore your system state data from a recent backup. The system state data for your computer consists of the registry hive files, boot files, and the COM+ Class Registration database. Using the Backup utility included with Windows XP, you can easily back up your system state or restore it WindowsDevCenter.com — How To Recover from Registry Corruption