Being in the middle of an attempt to re-boot my laptop, it has dawned on me that perhaps a background utility that checks the % of disks capacity could be a good thing to have on Zorin. It could be like the apps that check battery % preventing total shut down by alerting phone/laptop/desktop etc. users to charge up ('clean house' on computer) before disaster happens.
That is what is happening to me - my laptop's files got FULL, a brief notice flashed to 'empty trash' - to which I clicked (Yes/OK) and then my laptop became UN-bootable when I tried to boot it next time. An ounce of prevention vs. a pound of cure . . .
A major offender of drives so full they can't boot are log files. No one confirmed I was understanding correctly, so I didn't write a proper tutorial, but based on what I understand, you can significantly limit how much log file the system is allowed to generate.
Not to imply that a low space warning wouldn't also be good; other things can fill a disk too, after all.
It's a good time to ensure you install Stacer. Even though @sandbill can't boot his existing installation he could use live boot to recover his data. Also always a good idea to use Disk Analyzer as given in the Unofficial Manual.