When installing Simconnect, our installer doesn't do anything strange or unusual. It simply launch the installer you have in your P3D folder:
\Lockheed Martin\Prepar3D v2\redist\Interface\FSX-SP2-XPACK\retail\lib
Assuming your P3D installation is complete and not missing anything and of course you haven't removed the Simconnect installer. Now, since that installer is not an .exe, but an .MSI file, it's POSSIBLE (assuming the file is there), you have a problem with the default Windows Installer libraries, that are present in every Windows system. In this case, the problem is not even flightsim-related, and it's something that must be fixed at the Windows level.
Do you have the Simconnect installer in that folder ? If yes, are you able to launch it manually ? If yes, we can then start troubleshooting why it's not running from the installer. If not, if the installer doesn't run stand-alone, it's nothing our installer can fix, of course.