we should be able to save you that
Did you try this?
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB << if you don't have one already
change boot order so USB is first, hdd second
boot from installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose advanced
choose command prompt
Type
bootrec /repairmbr and hit Enter. This will rebuild the Master Boot Record.
Reboot your computer and retest.
another option is system restore
boot from installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose advanced
choose system restore - hopefully there is a recent date to pick, this will roll system back to that date and hopefully fix this for you.
if neither of those help, we can try a factory restore which will hopefully reinstall all the pre installed software you had
is there anything on C drive you want to rescue? try making this on another PC: http://www.howtogeek.com/howto/windows-vista/use-ubuntu-live-cd-to-backup-files-from-your-dead-windows-computer/
boot from installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose reset this PC
Should be an option for factory restore here, it will wipe entire PC and set it back to how it was when you got it
Also, you don't need your licence code anymore. If win 10 is currently activated, it will always reactivate on that PC again, Microsoft have details of PC + licence on their servers, if you reinstalled win 10, and got to screen asking for licence, you click "I don't have a key" and it will continue install and auto activate once complete.The silly shop should know that, or perhaps they do and just want your money...