There's no need to Deactivate before changing hardware. You do it in order to not waste 1 activation, but it's not that if you don't Deactivate, the software won't run. Unless, of course, you have already used all your activations but, again, it's not that the software will not run, you will see a clear message about having used all your activations, and the sceneries will work normally, but in Trial mode.
I tried reinstalling addon manager but this does not work. I get messages about hardware changes and corrupt bglmanx.dll files
Have you just reinstalled it from an installer you already had, or you *downloaded* now, and installed it ? If not sure, download it now, to be sure you have the latest version.
And, if you see any errors, clearly and precisely indicate the exact text of the error.