Scenario 1: after PAEPATCH 32Bit Windows to use more than 3.5 GB or RAM, sometimes Startup becomes corrupted. Thus, one must follow procedure to fix Window’s Master Boor Record (MBR):
 
1. Fix BCD <——- Confirmed as Effective Procedure!
https://login.microsoftonline.com/common/oauth2/v2.0/authorize?client_id=a81d90ac-aa75-4cf8-b14c-58bf348528fe&redirect_uri=https%3A%2F%2Fanswers.microsoft.com&response_type=code%20id_token&scope=openid%20profile&state=OpenIdConnect.AuthenticationProperties%3DCc2acjNm7LOQWJ57spjEmIn0txqXJO_rw_TIWsY1EEmZtXKC7RqbR74YZ0H7G2MxeuMI4Z7dFYoNOlVmKBzw79cY829HIx_xnd0vONljtYlLd3p9Ii4MuFQI5On8I7S_LBHA9ZWsrO8GP_1AZZg6bDrYXGOzAz7Cr-EqdUXeA9_fScBN2qypya6JwvvBEBmKKMHk1dMP5OIfx_7jkEdsCmXIT48jxb90rucVFFJy3HKLmF7cGWXByu66Wrtnmt6u6V7NccNjNOJ3mUxXRFtsBGa7MqfdlhIlpHhrfzgTOxrk9OQaIn21CUDnDQtwEyfNOe4t5DWQIebaw8B2hI-x7pTuI-8i6m76wf58Qzfl-bTQomSANqFNo6P-r1X891NX&response_mode=form_post&nonce=638636472684957816.MWJjZmIyYTktZTA2Zi00ZjMyLTgxOGUtNmJhNDdmNzliYjlhMzM1ODQ1ZjAtMmQ3MS00MzEzLTgxMTAtODRjZmRlNGM0OTAz&nopa=2&prompt=none&x-client-SKU=ID_NET472&x-client-ver=7.6.0.0)
     a. start with Windows CD/USB and choose recovery options
     b. CMD> bootrec.exe /FixMbr
     c. Rebuild BCD:          
    • bcdedit /export C:\BCD_Backup
    • c:
    • cd boot
    • attrib bcd -s -h -r
    • ren c:\boot\bcd bcd.old
    • bootrec /RebuildBcd
Scenario 2: after a registry edit, Windows could not start. One must try the following procedure:
 
2. Restore registry ) using commands
     Run these commands in recovery console
          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
     Reboot | Press F8 | Enter Safe Mode
          Tools | Folder Options | View tab | Show Hidden Files and Folders
          Find Restore Point Folder, which always start with “RP”
          Open “Snapshot” folder and copy the following into C:\Windows\Tmp folder and rename them:
          _REGISTRY_USER_.DEFAULT (rename to DEFAULT)
_REGISTRY_MACHINE_SECURTY (rename to SECURITY)
_REGISTRY_MACHINE_SOFTWARE (rename to SOFTWARE)
_REGISTRY_MACHINE_SYSTEM (rename to SYSTEM)
_REGISTRY_MACHINE_SAM (rename to SAM)
Restart and go back to Recovery Console
           del c:\windows\system32\config\sam
del c:\windows\system32\config\security
del c:\windows\system32\config\software
del c:\windows\system32\config\default
del c:\windows\system32\config\system
copy c:\windows\tmp\software c:\windows\system32\config\software
copy c:\windows\tmp\system c:\windows\system32\config\system
copy c:\windows\tmp\sam c:\windows\system32\config\sam
copy c:\windows\tmp\security c:\windows\system32\config\security
copy c:\windows\tmp\default c:\windows\system32\config\default
Restart and perform System Restore          
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