Monitor keeps turning itself off randomly

So, here’s the deal... I was playing this one pretty demanding game I've been into lately, and out of nowhere, my monitor just went black. I tried restarting everything, but now the computer won't even boot up. It started with a Blue Screen of Death showing some kind of display error, but now it won't even get that far. It refuses to load Windows, won't enter Safe Mode, and can't even trigger the Windows repair tool. I even tried booting from a USB drive to reinstall win, thinking maybe the OS just completely crumbled on me, but nothing works. I'm honestly stumped. I know the RAM is fine because I actually swapped it out to check. At this point, I'm wondering if it's the motherboard, maybe an issue with the GPU, or perhaps the hard drive? Does anyone have any expert insight on this? ;3 It managed to hit Safe Mode once at first, but now it won't even do that anymore.

Can you at least get into the BIOS?

Your GPU might be dead or partially failing.
If you're on a desktop, try swapping in another card. It's always worth testing with an old pCi-graficka if you have one lying around, rather than messing with PCI-e or AGP right now.

It's also possible your power supply is shot and isn't delivering enough voltage on the 12V rail.
Check your BIOS settings to see if you can monitor the voltage levels; it shouldn't be dropping below 11.40V.
Alternatively, just use a multimeter to test the yellow wire or contact against the black wire or the chassis.

So, I finally figured it out... turns out my graphics card is acting up. I can't quite put my finger on what's actually broken, but everything runs perfectly fine when I swap it out for another one. Honestly, I have this nagging feeling that the VRAM might just be giving out on me.