Respuesta a "My MBP won't boot, with horizontal line at apple logo"Hi I know I'm a little late to the party, but I had this problem, found this thread, and ultimately solved my issue. The root cause for me was a POS (Piece of ...) Radeon display controller. Google "radeongate." Late 2011 MBP. 15". I took it to the Apple store. They ran a diagnostic. Told me that my video chip was dead and I needed to a new system control board. "Unfortunately, we no longer carry those..." Ebay: $450. Screw that. I was just about to bake my system control board in the oven when I did a verbose boot and googled some of the messages I saw. I ended up finding realmacmods. This process worked for me when all the PMC PRAM etc wouldn't. https://realmacmods.com/macbook-2011-radeon-gpu-disable/ At the bottom of that link is a permanent (disconnect a component from the board) solution that I may do if upgrades start failing. Good luck.