I actually had got it running in Windows 8.1 flawlessly that one time. I played various games on the external and the internal 1600p display. (Optimus worked.) At that time I had the GPU directly on the 16x molex-powered riser. Then I plugged a 90° riser to the molex-powered riser and the GPU onto the 90° riser. Power on procedure is the same one as shown in your first post. After that I rebooted the MBP and then there was an error and Windows couldn't be booted at all. Apparently some files in the /Windows folder was broken, so I had to fresh install Win 8 again. Windows recognised the card as a "basic display something" (can't remember), so I installed the latest Nvidia drivers and rebooted. At the option-menu I plugged in the eGPU and both displays are black and only the keyboard is backlit. I have to power off while holding the button I will follow your suggestions and we'll see what happens. Edit: I rebooted the MBP without using the option menu and with the eGPU plugged. Device Manager shows the GTX 960 with a yellow exclamation mark on the icon. Device status in the properties tells me that "Windows has stopped this device because it has reported problems. (Code 43). Rebooted again (same thing. plugged in and without option menu) and black screen. 2. Edit: Plugging in the eGPU inside Windows and trying to install the Nvidia drivers doesn't work. "Graphics driver could not find compatible graphics hardware." Plugging the eGPU mid-boot isn't working aswell. Windows doesn't recognise the eGPU in the Device Manager. Cant install drivers. Same as above. 3. Edit: Turns out I plugged the 8-pin power connector wrong. But that didnt change the problem. Next morning I tried other Thunderbolt ports on both the MBP and the Akitio board and now the GPU works when I boot without the option menu. After a few reboots: black screen again. Sometimes it works, sometimes it doesnt.