Okay I’m home.
I turned it back on. It’s back to the ~6.5 minute boot time that I originally had the problem with. It loaded fine at first, displayed the Windows Live background thing, I put in my PIN to login, etc.
I saw the outline of my desktop and icons for a few seconds and then it went back to the black screen, which is how it still is now. I get a cursor with a blue loading wheel if I move the mouse, and I know the display is on, because it’s a bit lit (not like a powered off screen) but otherwise nothing. It’s been black for 8 mins as of this post.
Edit: it’s now been 40 mins. Still black, still a cursor when I move the mouse