[SOLVED] PC suddenly stopped displaying boot screen and BIOS

[Lernos1]

Hello. I'm running a Windows 10 (20H2) PC with an Intel Core i5 , 14 GB RAM and an NVIDIA GeForce GTX 1060 3GB. I only have one monitor, iiyama ProLite E2003WS, and a DVI-D cable to connect to my graphics card. The PC has served me well for a couple years already. However, today it suddenly stopped displaying my boot screen with American Megatrends messages (no signal) and if I'd enter BIOS by pressing Delete, there would also be black screen forever. However, booting into Windows (including blindly pressing Esc, then Enter to exit BIOS) works just fine, the monitor suddenly gets the signal back and displays everything. What I've tried so far:

Updating graphics card drivers using NVIDIA GeForce Experience - didn't help
Installing the "NVIDIA graphics firmware update for displayport 1.3 and 1.4 displays" - didn't help
Turning everything off, disconnecting all cables, removing every power source connection and waiting for 10 minutes - didn't help
Connecting the cable to the onboard graphics port - works and shows both boot screen and BIOS, but is extremely inconvenient

What do I do to get it back to how it used to be?

 

[Lernos1]

SOLVED. Turns out, there's a setting in the BIOS (in mine, it was Advanced - Configure Onboard Devices - Onboard VGA Config. - Primary Graphics Adapter - change "Internal VGA First" to "PCIE VGA First") that makes the motherboard's graphics processor "hoard" the channel on startup. As for why the change was so sudden, I suspect it's the default setting, and my CMOS battery just died. Let this be an advice to future generations then! Maybe even put it into the checklist of things to do before asking questions, idk.