PITA but,
I would uninstall all Nvidia drivers, let the machine default to the windows defaults.
Uninstall the 970, reinstall the old card, let machine boot to windows drivers.
Uninstall the old card, reinstall the 970, let boot to windows drivers.
install 970 drivers for you system, only install the driver and PhysX, nothing else.
If you use an HDTV as a monitor, try all the card dance using an old analog monitor or d sub connected. Something I ran into, but explanation winded.
Make sure you choose clean install.
make sure all plugs to card seated right, that card is seated right, that its fans are functioning.