Q: External Screen goes on sleep mode after plugging it in

Hi kibstr,

I understand your Macbook Pro knows you have connected your extertal display but the external screen(s) stay black. They go to sleep as if not getting a signal.  Good job testing with another cable and display.

There's a troubleshooting section "If the display image is blank or unusable" in this article:

Get help with video issues on external displays connected to your Mac - Apple Support

Although you have tried some of the steps, please try the other steps.

Thank you for using Apple Support Communities.

Howdy kibstr,

Thanks for going through the article. If you have gone through all the troubleshooting there is that last step.

Get more help

If you've tried these steps and your display still isn't working, contact Apple Support to get more help. 

Diagnostic fees may apply for issues not covered under warranty or the AppleCare Protection Plan (APP).

Let us know what you find.

Hi kibstr,

Try this link, Contact Apple Support

Take care.