did you upgrade to win 10 or fresh install?
have you got a win 10 install USB or DVD? You can get it from here:
Windows 10 media creation tool Run that and it lets you make a USB or DVD - obviously you need to run this on another pc.
change bios boot order so its USB or DVD first, hdd second
boot from installer
on screen after language choices, select repair this pc, not install
select troubleshoot
select advanced
select start up repair - this will scan pc and maybe the blank screen = will ask for logon
another thing that can fix this is boot into safe mode
boot from installer
select repair this pc
select troubleshoot
select advanced
select start up options
select 4,5 or 6 (they all safe modes)
boot into safe mode, restart pc (Yes, just going into safe mode can fix this)
if neither fix it, we can try a reset
before we do anything, d/c any extra hard drives from pc as it may wipe them all
boot from installer
select repair this pc
select reset - two options, keep files and settings, or wipe it all - i would take first
now if you get an error saying drive is locked, follow this:
http://www.thewindowsclub.com/the-drive-where-windows-is-installed-is-locked