If you can't get into a location with a command prompt:
Make a bootable Windows 10 USB stick from another computer (
download the Windows 10 media creation tool)
Boot from it.
Next your way through until you see "repair existing installation", click that
If you've already tried startup repair and that doesn't fix it, you are going to want to get a command prompt and run some commands to:
1. Check the health of the hard drive
2. Restore the consistency of the Windows installation
3. Repair the integrity of the windows image if #2 doesn't work
Step 1:
So, once you get to a command prompt, run: chkdsk /f c: (assuming c: is your windows drive letter when booted from USB, you can verify this by going to c: via cd c:\ and issuing a dir command and ensuring that what you see, is what you expected to see on c
If it fixes some stuff, you might want to do a chkdsk /r c: to check for bad blocks
If things were fixed, try booting windows now. Does it boot?
If no corrections were made to the file system or it doesn't boot, proceed to the next step.
Step 2:
run sfc /scannow with switches to tell it where Windows is:
sfc /scannow /offbootdir=c:\ /offwindir=c:\windows (both of these assume Windows is still on c: when booting from the USB, if the drive letter isn't c, adjust accordingly)
Did this repair things? If so, try and boot. Does it work?
If this doesn't fix it, or it was unable to make the repairs, move to step 3.
Step 3:
Restore the health of the system image.
DISM /Online /Cleanup-Image /CheckHealth
DISM /Online /Cleanup-Image /ScanHealth
If these show issues with the image, then run:
DISM /Online /Cleanup-Image /RestoreHealth
If that fails, we'll need to change where it pulls the image from, but we'll leave that for now.
Once the RestoreHealth process is complete, run the sfc command again, which should be successful this time.
Now, if you CAN get to a command prompt without the USB, run the above commands from that command prompt, but sfc can be run with just sfc /scannow as you shouldn't need the drive letter flags.