What version of Windows? Are you running any particular app (eg, gaming, playing vids etc) when this happens or is PC sleeping? "Second port on the NVidia card" doesn't mean anything to us. What type port is this, HDMI, DP, DVI etc...? Can you test this monitor on different PC or different monitor on this PC? Try physically removing the NVidia card (see Service Manual) and connecting the monitor to one of the onboard video ports (HDMI or DP), preferably using the same type port you use now on the video card, if available  Then use the PC that way for a while to see if that solves the problem. Note: You can't just move the monitor cable from the NVidia card to an onboard video port without removing the card. The onboard ports are disabled while the card is installed. These tests should help you figure out if this is a monitor or video card problem, etc... Edited
Hello  I have a problem with my Dell monitor P2418HT where it loses video signal from the PC. It happens regularly and the only option for me is to switch off the mains power and reboot the PC. I am using an NVidia card and the cable to the monitor is connected to the second port on the Nvidia card to the monitor. Nvidia GE Force GTX 1060 6GB. I would be grateful for some suggestions.  Thank you Manogaran   
Dell XPS 8920 and Dell monitor P2418HT