Please clarify what do you mean with "I had to reinstall FSX_SE, I installed it into a different hard drive". If you moved it manually, nothing will ever work, because the FSX registry keys are still pointing to the old folder.
Also, if you once had FSX standard, then you removed it, you should also uninstall/reinstall FSX:SE again, because the sim it's configured in two different modes, depending if you had FSX standard at the time of the FSX:SE installation.
Changing from a dual FSX+FSX:SE installation to an FSX:SE only installation cannot be done by simply uninstalling FSX. The proper procedure to switch from FSX+FSX:SE to FSX:SE is:
1) Uninstall all your add-ons from FSX
2) Uninstall FSX. Remove the old FSX folder too.
3) Uninstall all your add-ons from FSX:SE
4) Uninstall FSX:SE. Remove the FSX:SE folder.
5) Reinstall FSX:SE and run it at least once, this is required, in order to have all the registry keys set properly, which is only done by Steam after you run the game at least once, and it will configure to run FSX:SE in its "Single" mode with no FSX installed, posing as FSX.
6) Install all the addons in FSX:SE.
