The Windows Registry Checker Tool (Scanreg.exe) was included with Windows 98 and Windows Millennium Edition. Scanreg can back up, restore, optimize and fix the Windows registry, which stores operating system and application configuration settings. Windows automatically backs up the registry each day and restores it as needed, but in some situations you might have to fix or restore the registry yourself.
Restart Windows by clicking "Start," "Shut Down," "Restart" and "OK."
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As the computer starts up, press and hold the "Ctrl" key on your keyboard. You should see a menu showing various startup options. (If you don't, you might not have pressed the key soon enough. Restart the computer again.)
Select "Safe Mode Command Prompt Only" with the arrow keys and press "Enter."
Type "cd\windows\command" at the prompt and press "Enter."
Type "Scanreg.exe /restore" at the command prompt and press "Enter."
Select a registry backup from the list with the arrow keys and press "Enter." (Choose the most recent backup that was saved at a time when you weren't experiencing the problem you're trying to solve.)
When the registry has been restored, restart your computer by pressing "Enter."
Consult Microsoft's official documentation for a list of command-line options supported by Scanreg (see Resources).