I'm running windows 10 on my Macbook pro(2015) When i try to connect a secound screen, through VGI/thonderbolt adapter, nothing happens at all. When doing the same in OS it work fine. What can be the problem here?

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Have you already installed the Boot Camp drivers in Windows? They are needed in order to use the Thunderbolt port properly. If you have not installed them, boot up in OS X, open Boot Camp Assistant (in /Applications/Utilities) and tick only the option to download the "Windows support software". You need a USB drive to save the software. Then, boot up in Windows and run the Boot Camp installer from the USB drive.

(If you installed Windows from a USB drive and you used Boot Camp Assistant to create the Windows installer, you may already have the drivers on the USB drive. Just open Windows Explorer, go to your USB drive and look for a folder named "BootCamp". Then, open it and run the Setup installer).

Hey!

I've installed Windows 7 & 8 on my Mac before using VMware, it is not the best but it did the job.

I'm guessing since that the OS X and Windows are two separate os(s) there are different settings, try adjusting the settings on the Windows machine.

Good Luck! 🙂