I have a couple of ideas that might help solve a couple of the issues. Have you made sure that the 7500 is still working on like a different computer?
With everything the normal way, that is without any other video cards does your computer boot normally?
I would recommend not trying to plug anything in your computer when it is running that is a disaster waiting to happen.
You can always go here
and then download the drivers, then try to install the drivers after the card has been installed.