monitor on my PC keeps turning off and on intermittently. Through a process of elimination I have worked out it's not the cables or the monitor

Hi, Scott Williams

Welcome to Microsoft Community.

We understand that you have encountered the problem that one of the monitors of your computer keeps turning on and off. If the cable and the monitor itself have been ruled out, then you need to investigate the interference of drivers, systems and third-party software: 

1. Update the graphics card driver:Open Device Manager, find the Display Adapter, right-click your graphics card, and select Update Driver.Or visit the graphics card manufacturer (such as NVIDIA or AMD) in official website to download and install the latest graphics card driver.2. Adjust the power management settings:Open the Control Panel and select Power Options.Be sure to select a "High Performance" power plan.Click "change plan settings"-> "change advanced power settings" and ensure that "PCI Express- link state power management" is set to "off" in power management.3. Check the external devices and ports:Try connecting the monitor to a different video card port to see if the same problem will occur again. Determine if the problem is with a specific port.4. Adjust the display settings:Right-click the desktop and select Display Settings.Make sure that the resolution and refresh rate settings of the two monitors are the same.Check whether the monitor is set as the main monitor, and try to switch the settings of the main monitor to see if there is any change.5. Check the graphics card slot and hardware connection:Turn off the computer, unplug the power supply, and open the chassis to check whether the graphics card is correctly inserted into the PCIe slot.Reseat the video card, make sure there is nothing wrong with the video card slot, and check for dust or loose connections.6. Check the situation of insufficient power supply:Make sure that each monitor is connected to a separate power outlet to eliminate power supply problems.7. Detect the temperature of monitor and graphics card:Use hardware monitoring software (such as HWMonitor or MSI Afterburner) to check whether the temperature of the video card and monitor is too high. If the temperature is too high, it may be necessary to improve the heat dissipation.8. Execute clean boot to troubleshoot the interference of third-party software:How to perform a clean boot in Windows - Microsoft Support*Disclaimer: Clean startup is to start Windows with a minimum set of drivers and startup programs, so that you can determine whether the background program interferes with your game or program and help you find out the cause of the problem. The steps of "clean startup" may be complicated at first glance, but in order to avoid causing you trouble, please operate it step by step in order, which will help you get back on track.*I hope these steps can help you solve the problem that the monitor keeps turning on and off. If the problem still exists, you can consider contacting professional technical support for further diagnosis. Please feel free to ask any other questions.

Best Regards

Nicholas.Z| Microsoft Community Support Specialist