My macbook pro doesn't detect external monitors

I can't find a link to the Belkin ThunderBolt-3 to ThunderBolt-2 adapter, but the Apple adapter like that carries a specific disclaimer that is does not provide a usable display signal of any description.

In general, you need to convert from the computer port to the display port using ONE adapter -- "stacking" adapters almost never works.

Apple does not make any DisplayPort adapter at this writing, but both full-size and Mini DisplayPort adapters are readily available for not much money.

Be cautious about ordering from Amazon, however. Some of these parts are mailed directly from the Far East and really will take three weeks to arrive.

Use multiple displays with your Mac

Highlight: Laptop lid must remain open during startup until I see desktop. Then both externals gets activated, before I can close the lid and force output to my dual external monitors only (connected via Apples HDMI to displayport cable and another regular HDMI).

If I restart with dual external monitors and closed lid, only 1 monitor activates next startup. It does not matter how many cable unplugs and force detection, resetting PRAM etc. I usually have my lid open as it is better for the fans during high workload. My laptop screen is so broken that I can't literally see anything but brightness and flimmer. I also use SwitchResx to get better resolution and I thought that was the main issue. It was not.

Restarting with both monitors and closed lid = only one gets activated and favours the right hand HDMI output IF both externals are connected. It works as usual when only one connected.

To activate the other external again, I have to shut down and open lid. Restarting only just gets into a loop. I have not discovered this until now because I rarely need to restart or shut down, and I keep mixing with number of screens. I can't force any detecting irregardless of unplug/plugging, put to sleep on/off and other various display or energy settings.

macOS High Sierra 10.13.3 (clean install as of yesterday)

MBPro (Mid 2015)

If you choose to use External display(s) with your MacBook Pro closed, there are certain ceremonies you must follow:

when starting up, when shutting down,

when entering sleep, when waking from sleep,

when closing the computer, when opening the computer,

when disconnecting displays

Failure to follow the correct procedures can easily yield a blank display.

These procedures are detailed in this article.:

Use your Mac notebook computer in closed-display mode with an external display - Apple Support

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I also have this problem. If i startup my MacBook Pro 15 mid-2015 with the lid closed, connected to power with external mouse and keyboard it will only recognize one external monitor, not two. I have tried HDMI, Displayport, Detect displays, etc in all combinations but nothing works. There is a quick flash on the first monitor when you plug in the second, but it does not recognize it.

This worked before one of the High Sierra system upgrades in the last month or two...

If I start the MacBook with the lid open and connect both the displays before closing the lid it works fine. I had used a USB to HDMI adapter on this computer before the OS update caused this problem, but have removed the drivers for this adapter and do not use it anymore since having this problem.

I have tried all the SMC resets, PRAM resets, turn bluetooth off, reload OS and more with no success.

I have now tried a safe startup and the computer functioned normally. So I went and removed all the .kext files that I could determine were not part of the Apple install and not needed. No luck as it still only works if I have the lid open when I first startup.