Win 10 freezes up after bootup

[RRRSR]

HP Desktop with Win 10 as Upgrade from Win 7. No touch screen.

Was working fine since upgrading from Win 7 then started goint into 100% disk problem. Made changes to notifications as suggested in various fora. Things started going downhill from there.

Now on a fresh boot I get to the Windows desktop wallpaper, use the mouse to get to the pin entry, wait for a very long time after typing in the pin, and screen goes back to desktop wallpaper. Mouse is only thing that works. CTL ALT DELETE doesn't work. Nothing works.

All "solutions" I have read to date expect me to go into the settings and do stuff. I cannot get to settings or task manager or anything. I just have a pretty glowing paperweight that consumes electricity and takes up space.

I have no idea how to get into safe mode with windows 10. All the "advice" involves going into safe mode from a functioning Windows 10. My PC has only a frozen windows 10. No combination of mouse movements, key strokes, and/or curses makes any impact on the PC - it just sits there displaying the wallpaper.

 

[Trouble]

Don't login or type your pin or do anything else from the sign-in screen except access the power icon and choose restart while holding the shift key on your keyboard.
Navigate through the Troubleshoot / Advanced Troubleshooting screens to "Startup Settings" click restart when that option is made available and then choose #4 when the boot options are presented.
That should get you into safe mode.
From there, I would strongly recommend backing up all your critical data to an external resource.

Failing that you may need to boot from the Installation Media.
https://www.microsoft.com/en-us/software-download/techbench
Choose Windows 10, the first item in the first drop down (not single language at the bottom)
Next choose your language and your bit version (32 or 64 bit to match your system architecture or in the case of an upgrade, to match your currently installed version of Windows).
That will provide an ISO that will upgrade (or clean install) either or both Windows 10 Pro and Home.
Once you have downloaded the ISO you can use ImgBurn to burn it to a DVD http://imgburn.com/index.php?act=download
OR
Rufus to burn it to a USB ThumbDrive http://rufus.akeo.ie/
When you've managed to boot from the installation media you need to click the Repair Your PC link on the second page after the Choose a Language and Keyboard layout page.
That should get you to the Advanced Troubleshooting options.