I'd like to start off where this whole thing started. I was browsing Facebook when I happened upon a link. I have no clue if this is the cause, but I would refrain from actually following it regardless: http://toy.tahitizap.com/3/
It came up with a page suggesting other sites, and shortly after leaving, the screen went black, and I was redirected to the lock screen. I promptly forced a PC shutdown and did a full system scan after restarting to no avail.
Now, though occasionally, it will do just the same, even when I'm using the PC: go black, and redirect me to the lock screen.