Okay, so I've spent almost the entire last day on this problem, and I've googled the crap out of it, I hope someone here can help me.
First off: Yes, I've cleared the NVRAM/PRAM several times and I've reset the SMC more than once too.
I have a setup with two displays on my desk that are connected to my desktop PC. I sometimes used one of those displays with my MBP via HDMI. A couple of days ago, I've decided to use both of those with my MBP and an external keyboard/mouse just to have a more tidy experience on my desk.
So I got two DisplayPort to HDMI cables to realise this extravagant folly.
Now, when I plug either of them in, nothing happens.
The (internal) display will flicker for a second, but the external displays are not detected. Neither via the old "hold option and click detect displays in Preferences->Displays" nor via "put Mac to sleep and wake it up". I've cleared the NVRAM and reset the SMC several times. I've booted up in safe mode and tried it. No dice. They don't show up in the system information box either.
To be clear, I'm not trying to connect both displays at this time. Neither of them works with neither cable.
The cables are not faulty, as I've tried both cables and both monitors with my MacBook Air Mid 2011, and they work just fine in all possible combinations.
Both displays work just fine with the MBP directly via an HDMI cable or with my mini DisplayPort->VGA adapter.
So, surely, it must be some software issue.
Now, I've tried to use one of those hellish cables to connect my MBP to my TV, and --voila-- it worked. So my MBP is indeed capable of using those cables.
So, I've ruled out
a) the cables
b) the displays
and c) the notebook as a source for my woes.
Neither is it the combination of a & b (works with MB Air), a & c (works with TV), or b & c (works via HDMI and mDP->VGA).
What am I missing?
Here's the displays, sorry for not including them in the original post:
- BenQ XL2411
- Samsung SyncMaster P2770
The TV that for some reason works with the cables and the MacBook is a Panasonic TX-32ASW504. I'll try and go around town and plug my Macbook into other people's HDMI to test out other displays.
I'm running macOS Sierra 10.12.2 on a MacBook Pro Retina 13'' Mid 2014.