Ok, so you have the Addon Manager menu, but you don't have the Couatl powered plugins menu. That's why XPOI doesn't work.
Can you please post the content of your %APPDATA%\Microsoft\FSX\EXE.XML file ?
Also, open your FSX.CFG with Notepad ( it's located in %APPDATA%\Microsoft\FSX\ folder ), and look in the [Trusted] section, if you have any reference to the couatl.exe file. If you have, remove the *whole* line that contains it, save the file, launch FSX again, and please note if you get a request to trust the Couatl scripting engine, and obviously reply Yes.
If you still don't get any request to start it, perhaps it's the antivirus blocking it. Try to exclude the whole FSX folder from scanning OR, exclude the fsdreamteam\couatl\couatl.exe file from scanning, and reinstall XPOI again, with the antivirus configured as such.