I created a new user account but I can not get FSX to run in it. I just get black screens and cant launch a flight, it wont load.
That seems to confirm you have some kind of trouble with accounts on your system: FSX doesn't have to be reinstalled to run in a new user account, because it would simply re-create its default preference files in the local folders of the new account at the first startup, and most of the important files, like the scenery.cfg or the scenery cache, are located in a shared folder ( C:\ProgramData ), so they are not user-related.
I'm sorry, but I really can't offer any other suggestion now, other than I'm sure your problem will go away at the next Windows reinstall.
Don't you have another PC to test FSX + GSX on ? That would at least prove you the problem is that specific PC installation. Don't worry about the number of activations, if you need some to test, I can add them to your order.