I get the Windows XP could not start because the following file is missing or corrupt: WINDOWS SYSTEM32 CONFIG SYSTEM. When I type copy c:windows system32 config system c:windows tmp system.bak I get the system cannot find the file specified.
More about :win professional x64 start missing config sys
put the X64 disk in the drive, start the computer, and do a repair install.
Look in this forum, fourth post from the top, for the directions.
The repair does not reformat the drive or erase your personal files.