Excellent progress. Uninstalled device, removed drivers, cleared out nvidia driver folder from c drive. Rebooted and have DP monitor without lines, have nvidia control panel and 2 monitors running. Pooter installed nvidia driver version 399.07 which doesn't appear to be very old so I'll keep it for the next few days...maybe for good if it all works ok.
Going to reinstall the RAM and gradually put things back, rebooting and checking.
Looks like a corruption of the nvidia files took place somewhere along the line.
Thanks FT and Crash