Have you installed any addon programs or planes recently? Specifically any that launch via the dll.xml file or have C++ gauges?
I'm guessing your problem most likely lies in a faulty third party addon running in-process (using a .dll file). You can check the faulting module of your FSX crash, by going to the Event Viewer -> Windows Logs -> Application, then looking for an error generated by FSX. This should tell you the name of the file (DLL or gauge) in question.
Anyways, try clearing out the [Trusted] section of your fsx.cfg, located in %appdata%\Microsoft\FSX. Next time you open FSX, you'll have to allow all the gauges and addons that launch alongside FSX again, so make sure not to allow the faulty module to run again.