If you cannot do a Shift+Restart (at any Power icon, even on the Sign-in screen) to get to the built-in Recovery Environment, then you must use the one on external media...
(1) The first step is to make a Win 10 Installation USB drive here...
https://www.microsoft.com/en-us/software-download/windows10
Download Windows 10 - Currently this is version 1809
Click the "Download tool now" button to get
MediaCreationTool1809.exe. Click that .exe, & follow the instructions under "Using the tool to create installation media..." in the above article. The important thing is to select the
Architecture (64-bit/x64 or 32-bit/x86) & Language
of the computer on which it will be used. The Edition to select is "Windows 10" (unless you are a Chinaman). That will deliver both Pro & Home editions (which is sorted out during/after the install).
(2) Next, boot to the Win 10 Installation USB drive from the BIOS Boot menu screen...
Plug it in. Turn on or reboot
the computer. At the manufacturer's logo screen, press & hold the key
that gets to the BIOS Boot menu, & select the USB drive from the menu.
https://www.sysnative.com/forums/hardware-tutorials/23010-get-access-bios-settings-boot-menu-f-keys-hotkeys-system-manufacturer-oem.html
Get access to BIOS settings & Boot Menu: F-keys/Hotkeys by System Manufacturer (OEM)
Note: That site is informative, but I know nothing (good or bad) about any downloads or links there.
(3) The next step is to be sure you have good backups of your user files & downloads...
https://answers.microsoft.com/en-us/windows/for...
Rescue Files when Windows won't start
After booting the Win 10 Installation USB drive, at the 2nd screen, select
Repair your computer (instead of to install). Also, plug in external storage. Click "Troubleshoot > Advanced Options > Command Prompt". Then enter
Notepad at the Command Prompt. In its File menu, select
Open. It gives you a mini-File Explorer. Set Notepad to display all file types with its
requestor at bottom right...

Copy files to external storage just as you would in File Explorer.
It may be slow, & you shouldn't try to open any files while doing it. Just copy/paste them from HDD to USB. The files you want are likely at
C:\Windows\Users<Your username>.