Your Windows operating system is not able to start because the file, [Windows XP] C:\Windows\System32\Config\System is missing or corrupt which indicates that the system registry hive is corrupted. To have it back up and running, during the start of the boot sequence you have to press the F8 key which takes you to a menu. Choose Boot using the last known good configuration option that loaded Windows XP operating system with the previous configuration files. The other way is to boot the system with the Windows XP Installation CD. Once you are in setup, start the Recovery Console. Type in the appropriate commands and press enter after every line. Also change the C letter in the commands with the drive letter for your Windows XP operating system.