That had happened to me once, due to faulty RAM.
I forget the exact commands, but I'll check on the Phabricator, where I had posted about this back then.
Edit: It turns out that I had posted something unrelated, and when this had happened to me, I had done something else, which I do not currently remember.
Hopefully this bug report/thread on the Phabricator should help.

    Thanks a lot for your help, I've tried a little bit of everything without success... The good point is that I can access my hard drive through Live Solus and get back all my data.

    Will a clean install of Solus solve the problem? Because if that's the case, I just have to save my data on my external drive and reinstall Solus.

    Thanks again brent and moriel5

          DrGouh Unless you have faulty hardware, OS reinstallation should resolve the issue.

          Can you please verify that the RAM is functioning properly though? You can boot MemTest+ from a disk, or boot it from one of the Ubuntu disks to check this.
          RAM testing should be done one DIMM (stick) at a time.

            fsck the partition.
            partition must be unmounted, so it has to be done from outside the OS, like from livecd or another OS.

              gohlip Thanks, I had completely forgotten about how fsck works, since I had only used it twice in my life.

                My issue is now resolved, fsck didn't work because I was doing it on the wrong partition (yeah I know sorry for being dumb). It finally worked after doing

                fsck /etc/sdm-2 (I thought it was sda...)

                I didn't run a memtest because I didn't manage to find the option to do it despite the tutorials on the web.

                Thanks again a lot everybody for the help!
                EDIT: How do I put [SOLVED] in the title please?

                My friend had this issue yesterday after an update +restart, FYI you can fsck the partition from the emergency mode so you don't need to use a liveUSB or anything. Looking at the report log it seems that systemd tried to mount his windows partition on /dev/sda2 which of course failed, I mounted and looked into his root partition on /dev/sdb2 and his /etc/fstab was empty which was odd. Unmounting and just running /# fsck /dev/sdb2 and hitting Y for the fixes and exiting emergency mode worked and fstab was populated after logging in when I checked again.

                To get the command options just use /# fsck --help

                10 days later

                Hello! I am new to the Forum and fairly new to Solus. I am encountering a similar problem to the others that have posted in this thread. I have tried to enter some of the commands that have been suggested but nothing really does anything. The computer was working fine earlier in the day and when I tried to login again it became unresponsive and rebooting put me into emergency mode. The following screen shot was obtained by using the journalctl -r command.