That error seems to be tied into linux which might be a left over of your install? i think what happened is your win 10 install is on a GPT disk and the boot loader is looking for an MBR system - GPT is the disk format win 8.1 is on that caused the problem
Today I am going for the g2ldr.mbr file missing while booting Kali Linux. Yes, many of you have faced this problem. This is because you have a disk partition on GTP format but Kali linux wants disk partition on MBR format.
does win 10 boot at all or you get that error? If win 10 boots up, from desktop, you could try two things.
1. right click start button
choose run...
type
msconfig and press enter
in next window, go to boot tab
click on windows 10 and set it as default and apply
this might not help, I wasn't sure if it was enough
2. go to settings/update & security/recovery/Advanced startup - press the restart now button
this loads advanced startup
choose troubleshoot
choose advanced
choose command prompt and type these 4 commands in, one at a time with an enter between each
bootrec /RebuildBcd
bootrec /fixMbr
bootrec /fixboot
Exit
restart PC and see how it goes
In some cases you may need to run some additional commands.
bootsect /nt60 SYS or bootsect /nt60 ALL
if win 10 doesn't boot up, what type of PC do you have? need to get into bios and change it so you boot off USB or DVD, what is problem there?