I’d suggest burning an ISO of Linux (really just about any live Linux) and familiarizing yourself with concepts like mounting filesystems, partitioning, GRUB/U-Boot and the like.

I’d recommend trying the following in this order (easy to most difficult):

1. Scan your boot device’s (hard drive) filesystems for errors with fsck and repair any errors it finds. If errors were found, reboot and see if the problem has gone away.
2. Check the boot device’s /boot partition. You’re going to be using any combination of fdisk, parted, lsblkid to figure out which partition is /boot, mount its filesystem, then move on to harder stuff.
3. “Harder stuff” is going to be finding out if the kernel is botched, and praying that an older one is available and figuring out how to boot from it. If there isn’t an older one, there’s a chance you can search for packages from your distro that include the kernel — I’d try to find an exact filename match and copy it over the existing one but maybe only after backing it up first.

This is where GRUB knowledge comes in handy and unfortunately where my advice ends, because personally I’m inexperienced in this area.

Another option which might be a lot easier (if you know what you’re doing) is reinstalling the OS completely after backing up everything.

Or, if you’re lucky your /home directory was created in its own filesystem in its own partition. Provided you set that up again without destructively destroying/partitioning it while installing the OS again you could very easily get a clean install with all your user-level apps’ preferences, downloads, etc. preserved.

Edit: Taking a look at your GitHub screenshot, my guess is that the three Linux-related lines on the boot screen are different kernel versions. It makes me think there was a botched update to your /boot partition (just because the names are exactly the same) though I could be wrong there.

It’s strange you have a Windows boot option if you don’t have Windows, but it would make sense if the Windows bootloader was there when elementaryOS was installed and the drive hadn’t been completely wiped beforehand.