If you have access to a working Mac, the next thing I would try (after what you have already done) is to start the troubled MacBook Pro in Target Disk Mode by powering on the computer and holding down the T key until the Thunderbolt (or USB) symbol appears on the screen. Then connect it to the working Mac, mount the drive, and use Disk Utility to to verify and, if needed, repair the drive. Also take this opportunity to make a copy of the drive in case (a) the drive is failing or (b) you end up with a repair that includes a new drive. Obviously if Disk Utility cannot repair the drive, take it to Apple for service.

If the drive appears good but the computer still will not boot, the next thing I would try is running Apple Diagnostics by turning off the computer, turning it back on and holding down the D key while the computer starts up. If any issues are found, Apple Diagnostics suggests solutions and provides reference codes. Take note of those reference codes and give them to Apple when asking for service on the computer. Note that you need to be connected to the internet to run diagnostics. If D does not work (possibly because there is something wrong with your disk drive) you can use Option+D to load the diagnostics over the internet.

If the diagnostics show nothing wrong and the Target Disk Mode show nothing wrong with your drive, I would be pretty surprised. In any case, having made a backup of the drive from Target Disk Mode, if Disk Utility did not get the drive back into bootable shape, I would take the computer to Apple for repair.

Stuck at the Apple Logo. What to do.

^{This is an attempt to write a canonical QA for this issue, as per the Meta post: Where is the list of canonical questions stored for Ask Different? I expect it to be periodically edited with the goal of becoming a comprehensive information resource.}

When you get stuck booting at the Apple logo, it can be really frustrating. All you've got is a grey Apple and (maybe, but not always) a loading bar that's stopped moving. The stuck logo means something has crashed and this Mac is going nowhere fast. This document is written to help you figure out what the problem is/could be and take the next steps to getting things resolved.

Start with Verbose Mode

Hold ⌘ Command V while booting. This will boot in a non-graphical mode allowing you to see the boot time messages as they scroll by. It's a good idea to have a camera recording this as it will capture all messages as it scrolls across the screen. What we want to do is see where things are crashing so we can take appropriate action.

Booting from Recovery (local)

When you boot from recovery, you are booting from a different boot partition on your drive. It's a clean version of macOS that will allow you to use drive utilities, open Terminal to run commands and even do a full re-installation of your operating system. If you can boot to Recovery, this means your hardware is likely good and you have a problem with the macOS installation itself.

Booting from Internet Recovery or via USB

You can boot into [Internet Recovery][inet-recovery] by using ⌘ CommandR or via a bootable USB device by holding ⌥ Option and selecting the boot volume.

The goal here is to eliminate your boot device from the equation. If you can boot from Internet Recovery or from a bootable USB, then you've narrowed down your issue to a physical problem with either the boot device (drive) or the drive interface (SATA, PCIe 2.0 interface). You may have to replace the SSD or hard drive depending on your Mac, but if the storage is integrated onto the logic board, it will have to be replaced.

However, if you are stuck here, you have a hardware issue.

Internet Recovery downloads the OS installer to memory - you don't even need a hard drive installed/attached to download and run the installer properly. So, if you're attempting to boot and it gets stuck, you need to look at hardware being the problem. Same with a USB installer - you're using the USB bus and not the SATA or PCIe interfaces bypassing the traditional channels from which your drive operates. If you can't get past this point, it's definitely a logic board issue.

Possible Diagnostic Tests

You can try a boot Apple Diagnostics by holding D while booting from a powered off state. However, Apple has been reducing the usefulness of this utility on newer Mac models. You're not likely to get much useful diagnostic data. You can try Memtest86. They have instructions to create a bootable USB, however, since all components are now soldered to the logic board the end result will be the same - the logic board needs to be repaired/replaced.

[inet-recovery]: