Macbook stuck on Apple Logo/loading screen

A Troubleshooting Protocol to Identify Problems or Fix macOS El Capitan or Later

You should try each, one at a time, then test to see if the problem is fixed before going on to the next.

Be sure to backup your files before proceeding if possible.

1. Shutdown the computer, wait 30 seconds, restart the computer.
2. Disconnect all third-party peripherals and remove any support software like drivers and plug-ins.
3. Resetting your Mac’s PRAM and NVRAM
4. Reset the System Management Controller (SMC)
5. Start the computer in Safe Mode, then restart normally. This is slower than a standard startup.
6. Repair the disk by booting from the Recovery HD. Immediately after the chime hold down the Command and R keys until the Utility Menu appears. Choose Disk Utility and click on the Continue button. Select the indented (usually, Macintosh HD) volume entry from the side list. Click on the First Aid button in the toolbar. Wait for the Done button to appear. Quit Disk Utility and return to the Utility Menu. Restart the computer from the Apple Menu.
7. Create a New User Account Open Users & Groups preferences. Click on the lock icon and enter your Admin password when prompted. On the left under Current User click on the Add [+] button under Login Options. Setup a new Admin user account. Upon completion log out of your current account then log into the new account. If your problems cease, then consider switching to the new account and transferring your files to it - Transferring files from one User Account to another.
8. Download and install the OS X El Capitan 10.11.6 Combo Update or 10.12.6 Combo Update or Download macOS High Sierra 10.13.3 Combo Update as needed.
9. Reinstall OS X by booting from the Recovery HD using the Command and R keys. When the Utility Menu appears select Reinstall OS X then click on the Continue button.
10. Erase and Install OS X Restart the computer. Immediately after the chime hold down the Command and R keys until the Apple logo appears. When the Utility Menu appears:

1. Select Disk Utility from the Utility Menu and click on Continue button.
2. When Disk Utility loads select the drive (out-dented entry) from the Device list.
3. Click on the Erase icon in Disk Utility's toolbar. A panel will drop down.
4. Set the Format type to APFS (for SSDs only) or Mac OS Extended (Journaled.)
5. Click on the Apply button, then wait for the Done button to activate and click on it.
6. Quit Disk Utility and return to the Utility Menu.
7. Select Reinstall OS X and click on the Continue button.

You already tried repairing your drive and it didn't seem to note any issues.

Forcing a power down can result in a corrupted volume. Doesn't happen most of the time (usually self repairs at the next boot) but it can. I've had a couple of them myself. One was a drive that First Aid said was unstable and where I should offload data ASAP while I can. That drive when placed in an external enclosure sometimes mounts. I simply replaced it and kept around the old drive just in case I could get anything off of it that wasn't already on a backup. Another one was an external drive that I used for a bootable clone. It stopped working for clones after I got impatient and just unplugged it. After that every attempt to clone would end with an error that it was taking too much time and just ended without completion. First Aid (depending on the version - Recovery or from the boot drive) said that it completed with the volume fixed or there was no problem. The only thing that solved it was reformatting it.

I'd recommend just getting a new drive (maybe even an SSD) and starting with a fresh install of MacOS/OS X. Then you could see if you can offload data from your original drive in a USB enclosure. You could just reformat the drive, but from what you've stated I'm guessing that your data is more important to you than the cost of a new drive.