Boot the system.
Download the latest WHQL drivers directly from the AMD website, use the 'save' option for the download.
Uninstall the existing Nvidia drivers, and other Nvidia software, also any tuning software (Afterburner, EVGA Precision), and delete any saved profiles when asked if you wish to do so.
Shut down the system and REMOVE THE POWER CORD-there is a small, residual current supplied to the system by the PSU, even when it seems to be off.
Swap cards, connecting the monitor cable/s normally to the new card.
Reconnect the power cord and boot up.
The display will be VERY low resolution 800x600 or thereabouts-ignore that, it's just the Windows default drivers...Default resolution.
Install the downloaded drivers using the 'express' option.
The screen may flicker or go off-again, this is normal.
When the 'finished' screen appears, close its window and reboot.
You may need to go to the Windows Control Panel to adjust the screen properties, if needed, do so and reboot again.
Thank you mister. Very nicely explained!