Did you uninstall the old drivers completely before installing your new drivers?
If not download a program called DDU (Display Driver Uninstall), follow the instructions on how to use it. Here is a link to the download page:
DDU Download Link
Basically you uninstall the old drivers via Programs and Features, then reboot into Safe Mode. Once in Safe Mode, you run DDU and remove all traces of the old driver. Then reboot into normal mode and install your drivers. This should sort out any residual driver stuff from your 750.