I set up a dual boot Windows 8 & 10 system by initially setting up a dual boot with two Win 8.1 systems and then upgrading one to Windows 10.
Now I find that the Win 8.1 system fails at start-up with a message from GWX.EXE:-
"api-ms-win-core-heap-l2-1-0.dll missing"
And that's as far as it goes. I've tried a number of dodges but there is just no way I can get into the 8.1 system so it looks like none of the normal repair options are available.
I have tried the repair option from my 8.1 install disk but that takes me nowhere.
I also tried recovering the 8.1 system from a backup but the problem remains.
Since my Win 10 system can see the Win 8.1 disks, would it be possible to take advantage of that to fix the problem?