There are some quick tests that you can perform to rule out potential issues. Start by turning off all of the connected computers and peripherals, unplugging everything from the KVM, including power, and leaving it for 10 seconds. Then connect everything to the KVM following the procedure in the following FAQ: https://www.startech.com/faq/kvm-switches-setup.
You can test to make sure that the following components are working correctly and are not the source of the issue:
Video source (such as a DVR or computer)
Video destination (such as a monitor or projector)
Note: When you are testing your setup components, it is recommended that you avoid using any video adapters. For example, if you are converting a VGA source to HDMI to be used with an HDMI extender, you should test with an HDMI source.
To test your setup components, try the following:
Use the video cable, KVM switch, video source, and video destination in another setup to see if the problem is with the components or the setup.
Use a different video cable, KVM switch, video source, and video destination in your setup to see if the problem persists. Ideally, you should test a component that you know works in another setup.
When you test your cables, it is recommended that you do the following:
Test each cable individually.
Use short cables when you are testing.
When you test the video source and video destination, it is recommended that you do the following:
Remove the KVM switch from your setup and test to make sure that the video source and video destination work together without the KVM switch.
Test to make sure that the video source and video destination work together at the resolution that you want to use.
Note: In order for your setup to work properly, the video source, KVM switch, and video destination all need to support the resolution that you are using.