USB-C cable - Input Signal Not Found

[lwjz]

I have two HP Envy 34-inch Display monitors and I want to use USB-C and HDMI for dual monitor setup. My pc is a Dell Latitude 7400. The monitor works individually with a HDMI cable, but neither works with USB-C cable. The cable charges my pc with no issue when plugs in, and shows "USB-C Video: Connected" on first screen, then shows the "Input Signal Not Found" message then goes to sleep. Both monitors worked before, and still works with another pc. How should I fix this issue?

[banhien]

@lwjz 

Printers work with HDMI cable that means nothing wrong with them. The question now is: Does your Dell machine support dual displays From its specs, it has

1 Thunderbolt™ 3 with Power Delivery and DisplayPort
2 USB 3.1 Gen 1, one with PowerShare
1 HDMI 1.4
1 Optional external uSIM card tray
1 Optional Touch Fingerprint Reader in power button
1 DC-in 7.4 mm barrel

Please ask Dell: do those 2 USB-C ports (in red above) support video out ? Because many USB-C Gen 1 ports do not support Alt mode.

Regards.