No signal from display port

I just purchased and set up Dell U2719D dual monitors. The connection is a display port to display port to dual NVIDEA K620 video cards in a Dell Precision Tower 3620. OS is Windows 10, 64 bit with latest updates (Version 1803). All video drivers have latest updates. Computer power management is set to never turn off hard drives and monitors. When restarting windows or when powering off and restarting the computer, the monitors say no signal from display port and go into power save mode. I have to unplug new monitors, plug in older monitor (Dell U2515H) to same display port to get signal started from the display port, then I can unplug the older monitor and plug in the two new monitors and then they work fine. However, if I restart windows or power off then on, the new monitors say no signal at display port and go into power save mode. There is no option from the on screen display to turn off power save on these monitors. The DP cables are the ones that were in the box with the monitors.