Let's try simple. My kid's old machine did that when some scanners were plugged in. Since Windows has yet to boot it was not a Windows errrror.
In this case we got lucky and unplugging the USB devices let the machine boot.
After updating iTunes, I was surfing youtube. All of a sudden blue screen. When I restart, I get nothing, no bios, no splash screen. My monitors don't display no signal as when I disconnect the cable but their buttons do flash as if there was no signal. All I got is a black screen and no beeps.