Boot into Recovery Mode: reboot, and hold down the Left Shift Key. At the Grub Menu, select "Advanced Options"
From the recovery menu, select "fsck"
Follow the prompts. When it is complete and asks to remount - select "yes"
Reboot and test.
You will need to create or reuse a bootable copy on DVD or USB of Zorin OS (Or you can use another convenient distro).
You must unmount a disk before you can run fsck on it, which is why you must boot into a bootable medium. Boot up in Try Zorin, then open a terminal
Unmount your disk:
In your case, it would be
sudo umount /dev/sda2
Attempt fsck repair: EDIT (I originally wrote this out with the -p command. Just now, I actually zoomed into the OP's provided screenshot and noticed that the prompt states to not use the -p command. I am removing the command that I originally provided and replacing it with a manual fsck guide, instead.
Normally I would leave the original for posterity, but I remove it now to avoid confusion.)
fsck /dev/sda2 -y
If system boots up, open terminal and run
sudo apt-get clean
sudo apt autoremove
sudo apt-get update
sudo apt-get upgrade