Interesting, if there's not even the folder, it might be that Couatl.exe never started so, at least, this ensure that, whatever the problem is, is external to it, because it hasn't even got a chance to start.
Check the following things:
- You are not running FSX.EXE into any of the Compatibility modes. Right click on the FSX.EXE file, select Properties, check the Compatibility tab, everything should be turned off, which is the default setting.
You can try to activate the Simconnect diagnostic mode, this way:
Open notepad, and copy the following text:
[SimConnect]
level=verbose
console=1
RedirectStdOutToConsole=1
OutputDebugString=1
; file=c:\simconnect%03u.log
; file_next_index=0
; file_max_index=9
Save the file as SIMCONNECT.INI in this folder:
Documents And Settings\YOUR LOGIN NAME\Documents\Microsoft Flight Simulator X Files
At the next FSX launch, you should see a text window with diagnostic message, that should tell you what's going wrong. Let me know what you are getting, so we can have an idea what's happening.