I do not believe that a complete reformatting and reinstall of Windows and FSX does not function.
It should, but it might not be enough, all Windows update will probably need to be installed too.
@henoik:
You said you restored only your files from the previous install: check if you have a Simconnect.cfg under "My Documents\" (it's not really there, it's under one of the Flight sim sub-folders under "My Documents") and if you have it, REMOVE IT. That file is not supposed to be there on a default install, but if you restored your previous "My Documents" folder and this file contains a wrong configuration, you are actually restoring the bug.