El Capitan issues with External Monitor

Hello profaen,

Thanks for being a part of the Apple Support Communities! This is a great question and we’re glad you asked it! :)

If your Apple Display is flickering of turning off and back on there are a few different troubleshooting steps that I would first recommend. These steps are checking the connections, resetting the system, and resetting the resolution.

The following article has detailed information on how to complete each of these steps in the section labeled No video or no signal, image distortion, "snow," or flickering.

Apple computers: Troubleshooting issues with video on internal or external displays - Apple Support

We would like to hear back from you so you can let us know if these steps were helpful to you in resolving this situation or to provide more information. We are glad that you’re a member of the Apple Support Communities and can’t wait to hear more from you! :)

Have a great day!

Woot! Woot!

That is great to hear! We're glad that your display is performing now as it should!

As always, we look forward to your continued participation in the Apple Support Communities! :)

Cheers!