Also windows10 is running now smoothly.
Installed it without Bootcamp.
Note: that this MAC was already Partitioned by our IT guy using Bootcamp to use win8.1 and a Data partition.
And had also installed rEFINd, which i carefully killed somehow in time before.
As more and more customers are using win10 we also needed win10 on it. (we use this Macbook for testing purposes)
(First mistake was increasing the size of the Win8.1 partition within windows using Maigic Partitioning or something like it, this kills the ability to boot in MacOS ElCapitan. I had to restart with Command+R and could reinstall MacOS Sierra this way)
Jippeee! i could boot Mac again.
-So i splitted the data drive of 100GB in two equal halfs using gParted and formatted it.
-Then Win8.1 which was already on it would not start and started in some kind recovery mode, but recovery was impossible also using a recovery flashdrive.
-disabled SIP on this macbook, check the author's site of rEFInd for explanation on this.
-then had to use gDisk via the MacOS which i luckely still could boot and refresheg the Hybrid MBR with it
- I could boot Win8.1 again woohoo!
- then installed Win10 on one of the 50GB parts i created with a flashdrive
-used EasyUEFI to change the boot to Macos and restarted
-luckely rEFINd came up again
- now since i did not use Bootcamp, there is no possibility to install the correct drivers on Win10
- Found a program called Brigadier on SourceForge, this sees which Macbook you have and starts downloading the correct pkg from Apple
-rebooted into Macos again (because unzipping with 7zip within windows is a drama)
- used a little program which extract the pkg (just Google for it) (i also installed it on Macos by double clicking as first i did not know how to unpack it, but is probably not necessary)
- it unpacks the blablabla.DMG from the PKG
-then DOUBLE CLICK the DMG file
-copied the extracted files and folders from the DMG to USB stick and rebooted to win10 and installed them there perfectly
So now when choosing Windows in rEFInd i have to do it twice, because it will first ask which windows you want to boot, after choosing, choose the same windows icon again in rEFInd
that's it, piece of cake.....took me 2 nights and a day..........