Repairing a Missing Or Corrupt Windows\System32\Conf\System Files

This type of error usually indicated that the pc has refused to start because of a corruption within the registry. The following should remedy the problem. However, it is important that you replace all five registry hives. Simply replacing one or two could, potentially, cause other problems.

NOTE: dont use thses methods with oem versions

Easy Method

1. Restart your PC

2. Keep tapping the F8 Button until a menu appears

3. When the menu appears use the UP and DOWN arrow keys to select the ‘Last known good configuration’ option.

4. Once selected press Enter

5. Your PC should now reinstall the ‘last known good configuration file’

6. Restart your PC and see if the problem has been solved

7. If it hasn’t go on to the Harder Method below.

Hard Method

Step One

1. Insert the Windows XP CD into the CD-ROM and restart your pc

2. At the ‘Welcome to Setup’ screen press R to start the recovery Console

3. The Recovery Console will now open and the list of Windows installations will appear

4. As you only have one installation on your PC you need to press the number which is relevant to your installations location. This, obviously will typically be

5. When requested type in your Administrator password. If you haven’t set an administrator password, then simply press Enter

6. The Recovery Console command prompt window will now appear

7. At the Command prompt type the following, pressing Enter after you have typed each line. It is assumed that your root directory will be C: However, if your root directory isn't C:, for example, if you have other partitions.drives on your system you may have installed XP to say the D: drive, the you will need to substitute each reference to C: with the letter of your root directory.

md tmp
copy c:\windows\system32\config\system c:\windows\tmp\system.bak
copy c:\windows\system32\config\software c:\windows\tmp\software.bak
copy c:\windows\system32\config\sam c:\windows\tmp\sam.bak
copy c:\windows\system32\config\security c:\windows\tmp\security.bak
copy c:\windows\system32\config\default c:\windows\tmp\default.bak

delete c:\windows\system32\config\system
delete c:\windows\system32\config\software
delete c:\windows\system32\config\sam
delete c:\windows\system32\config\security
delete c:\windows\system32\config\default

copy c:\windows\repair\system c:\windows\system32\config\system
copy c:\windows\repair\software c:\windows\system32\config\software
copy c:\windows\repair\sam c:\windows\system32\config\sam
copy c:\windows\repair\security c:\windows\system32\config\security
copy c:\windows\repair\default c:\windows\system32\config\default

8. Now type Exit to exit the recovery console

9. Finally restart your pc

Source [Read More methods]