Black screen on startup following Windows 7 to 10 upgrade

Question

I have recently upgraded from Windows 7 (clean install) to Windows 10. The upgrade went without a hitch, and Windows started normally.

However, now the following happens:

1. I restart / cold boot the laptop
2. I get a loading screen with black background, blue Windows logo and spinner
3. I then get a completely black screen with no mouse pointer (even after 24 hrs wait)
4. I press power button, laptop sleeps, breathing light flashes
5. I press power button again, get blue screen with spinner, then login screen
6. I can log in normally and use Windows 10

So to clarify, with every single boot I need to sleep and wake the computer to get past this black screen.

I'm pulling my hair out with this, have read so many posts, and would be very grateful of any advice. Thanks in advance.