ASUS F17, black screen!

Hello,

After 2 years of use without any issue and in every way completely satisfactory on my Asus F17 PC until yesterday evening included, when I turned it on this morning, for the first time it did the black screen thing! Here is step by step what I discovered, as well as the little I tried:

1) I press the power switch (usual button) to start the computer; the "ASUS" brand appears followed by the text "In search of incredible" for a few seconds in the middle of the black screen (usual).

2) I have a Windows wallpaper photo (which changes roughly every ~3 days, usual) with the time written in white at the top, and below the date (usual).

3) as usual, I press any key on the keyboard to move to the next step (log in), where pressing a key: blurs the wallpaper photo (usual), shows the round photo of my avatar (usual), with my first and last name written below (usual), and displays the field to enter my PIN (usual).

4) as soon as I enter my PIN, it writes "Bienvenue" (usual), and instead of showing my usual desktop: a completely black screen!

BUT! The black screen, except:

> except the widget at the bottom right of my antivirus (BITDEFENDER), which has its normal and usual appearance, and that I can move.

> I have the mouse cursor visible, and I can move it normally.

> if I use the keyboard shortcut "Ctrl" + "Alt" + "Del" (which I obviously tried to get out of this problem), these 4 command lines appear on the black background (and it responds if I click one of them / I only clicked "Task Manager").

> I tried a keyboard shortcut with the "FN" key, i.e.: "FN" + "F9" -> it opens its little contextual window bottom right dedicated to screen sharing (with its 4 command lines), normal; I exit with Escape.

> and to shut down the PC: I am therefore forced to force a shutdown by a long press on the switch, AND THEN: it makes the upper half of the screen drop, the same wallpaper image as at the start (sharp), with a small white line at the bottom of the image: "Slide to turn off your PC".

> and I therefore have to click-drag this half of the image down to fill the entire screen, so that the computer stops (with its usual "shutdown in progress").

What is happening?

Why a black screen, when some phases show contextual windows, commands, the mouse pointer, even the wallpaper image?

Has anyone already had this problem?

Thanks in advance to the person who can help me regain normal use of my computer.