Explanation

Resolution
  1. Click Start
  2. Click Run
  3. Type Regedit
  4. Open the following folder:

**HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\SpecialAccounts\UserList**

  1. Right click in the open space to the left
  2. choose New
  3. Click DWORD Value
  4. Type the missing user ( Administrator, etc. )
  5. Enter
  6. Right Click on the user
  7. Change the Value data to 1.
  8. Close the registry
  9. Open the Control Panel and notice that your missing user has returned
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