Okay, I think it's really fixed this time. I decided I wasn't going to do updates until I knew for sure I could do so without crashing my computer, but I neglected to turn off automatic updates. So I was like "I'll show you, I'm going to put my computer to sleep and it'll never restart!" So I did that, but when I woke up this morning, my computer was ON and updates had been installed, but it's okay 'cause I could log in just fine. The problem has fixed itself.