CNG Service Defaults in Windows 7
Kernel Cryptography, Next Generation by Microsoft Corporation.
CNG is a kernel device driver. In Windows 7 it is being loaded by Boot Loader before Kernel initialization. If CNG fails to load, Windows 7 attempts to write the error data into Event Log and restart the computer, using the Last Known Good configuration. If the Last Known Good configuration is not valid, Windows 7 startup ends with a Stop error. If you remove or disable the CNG service, Windows 7 won't start.
Restore Default Startup Configuration for CNG
1. Select your Windows 7 edition and service pack, and then click Download.
2. Save the Win7_CNG_Service_Startup.cmd file to a local storage device.
3. Run the saved file as an administrator.
4. Restart the computer.
The CNG service is using the cng.sys file that is located in the %WinDir%\System32\Drivers folder. If the file is changed, damaged or deleted, you can restore its original version from Windows 7 installation media.