On next start of P3D V3, I can see couatl and prepar3d.exe in my task manager but P3D never comes up.
If P3D is on the Task manager, but it never comes out, it doesn't have anything to do with any of our products. The worse it can happen, assuming Couatl.exe is still running from a previous session (which doesn't happen if you quit the sim cleanly), is that no FSDT products will work on the next session, but this cannot affect the sim itself.
No, you obviously don't have to reinstall anything but, since some users make the mistake of trying to run the FSDT installer with the sim still running, there's a check in the installer that will automatically close any Couatl.exe that might still run, so this might be what fixed this.
- Restart Windows
- Start P3D, and everything will surely work
- Close P3D, and be sure it closes cleanly with no error messages.
- Go into Task Manager, and be sure that both P3D.exe and Couatl.exe has closed. If they are both close , it should be safe now to start the sim again. If they aren't, terminate them both from the Task manager.