1. Open up the Microsoft Management Console (MMC)
Start -> Run -> Type "mmc" (without quotes) and Click 'OK' or hit Enter on your keyboard.
2. Open 'Add/Remove Snap-in' Window
File -> Add/Remove Snap-in
3. Add the Certificates Snap-in
Click 'Add' then double-click 'Certificates'
4. Select 'Computer Account' and click 'Next'
Note: This step is very important. It must be the 'Computer Account' and no other account
5. Select 'Local Computer' and click 'Finish'
6. Close the 'Add Standalone Snap-in' window and click 'OK' in the 'Add/Remove Snap-in' Window.
7. Will now be returned to the MMC.
Install/Import the Root and Intermediates Certificate
1. Expand the Certificates section by clicking on the plus (+) sign and turn it to a minus (-) sign to expose the 'Certificates' tree.
2. Import the Root Certificate
Right-click on 'Trusted Root Certification Authorities', select 'All Tasks', then select 'Import'.
Locate the Root Certificate and click Next.
When the wizard is completed, click Finish.
3. Import Intermediate(s)
The process is the exact same except the area of interest is 'Intermediate Certification Authorities' instead of 'Trust Root Certificate Authorities' and the file(s) that are to be imported are the remaining files outside of your domain certificate.
4. Restart Website through IIS.