18.04 - Hang on boot prior to recovery mode

I'm dual-booting Windows 10 and Ubuntu 18.04. I recently updated Windows 10 and since then I have been unable to boot into Linux. Occasionally, updating has messed around with the linux partition booting but I have always been able to fix that via the grub command line. This seems to be an entirely different problem.

I apologize if this is a duplicate-- in all the related questions I've seen, the asker is generally able to reach the recovery menu, or can boot normally but not into recovery mode.

I can successfully start the boot process from grub, but after that point, I can't reach the login screen for Ubuntu. After entering grub (2.02) I navigate to either "Ubuntu" or "Advanced options for Ubuntu" and there I have four options :

Ubuntu, with Linux  4.18.0-21-generic
Ubuntu, with Linux  4.18.0-21-generic (recovery mode)
Ubuntu, with Linux  4.18.0-20-generic
Ubuntu, with Linux  4.18.0-20-generic (recovery mode)

Starting any of the four successfully exits grub and launches a cascade of screen output. However, I never reach a graphical login window, login prompt, or anything interactive. I will type out what are typically the last five lines here:

[   OK   ] Reached target Local Encrypted Volumes.
[   OK   ] Reached target Local File Systems (Pre).
[   OK   ] Listening on Load/Save RF Kill Switch Status /dev/rfkill Watch
[   OK   ] Reached target Sound Card.
[   OK   ] Found device WDC_WDBNCE5000PNC SSD.

And then, nothing happens. I have to hold the power button for six seconds to start the computer again. Short of a fresh install, does anyone have any ideas?

If anybody wants to know earlier lines, I'll be happy to transcribe them here. I'm grateful for any assistance I can get.

EDIT:
Here's what happened when I followed @K9spud 's advice.
fsck came back clean, so that's a relief.
I used chroot to use the linux installation as a root directory, and found that /var/boot.log progressed a lot farther than originally listed. One item I noticed was that the device at the end of the log as I posted it was failing to mount, probably because I set up /etc/fstab wrong. The last message in the log is

[  OK   ] Started Show Plymouth Boot Screen

After removing the offending line from /etc/fstab, the system boots normally.

TL;DR : Having an incorrectly configured /etc/fstab prevents the login screen from displaying.

This could be a difficult question to answer. The simplest answer is to install fresh, but that sucks if you have a lot of data/customization already invested in your old install.

If it were my machine, I would boot up Ubuntu in live mode from my Ubuntu USB install thumb drive and start poking around at the hard disk to try to figure out what has gone wrong and try to repair it.

First thing you might do is make a backup image of everything, since you might end up making things worse the first time around you try fixing things.

Next, I'd run fsck on the Linux partition to make sure nothing has corrupted the partition. If fsck comes back clean, great, all your data is still there and can be recovered one way or another if necessary. If fsck comes back with a bunch of errors, I'd say the installation is kaput, the partition is corrupted and not worth salvaging beyond any custom data you might be able to retrieve before doing a fresh install.

After fsck passes, I'd probably mount the Linux partition and use "chroot" to start working from within the Linux installation as if I had been booted from the Linux installation. You'll have to fiddle around with mounting dev, sys, proc, etc within the chroot environment, then you can run "update-grub" to try to get grub re-installed. Running "update-grub" might reveal some errors that could explain why you can't boot.

If "update-grub" works without revealing anything important, maybe try poking around under /var/log to see if any of the log files show any errors that could indicate why the system failed to boot.

Beyond that, I'm not sure what else to suggest without seeing all the error messages myself and trying to evaluate what is broken and what is not.

It is very frustrating that Windows has so little regard for Linux installations that it sometimes konks out Linux from booting -- makes me want to avoid having a dual-boot system with Windows at all. Hopefully Microsoft will improve and start being more careful about messing up Linux installations in the future.