Installation of Computer Security Certificate

We had a problem last time with the computer of my officemates.  He is from the Operations Group and we had to reformat his computer due to Windows error.  We had installed everything but his internet connection to a particular website is not working.  I forgot that it uses a Computer Security Certificate before you can connect.  Its been a while since we the first time we installed that certificate.  Good thing he has kept it in his drawer.  I installed it and then he now can connect to the site successfully and securely.