Quoting: ExpalphalogComputer was running fine last night. Did not download anything or change any settings.

This morning, when I log in my desktop background appears for a split second and then vanishes along with the taskbar. My icons are all still there. Any clues?

I know you said you didn't change any settings, but did you perhaps update your Nvidia driver to the new 390.12 beta? Try switching to a different TTY with Ctrl+Alt+F1 or something, then back to your X session, probably Ctrl+Alt+F7. My Xfce session only shows a few icons on a grey background until I do that. Haven't bothered downgrading the driver yet, as I only start my gaming box maybe a couple of times per day. Also haven't had time to investigate if this can be worked around somehow.

EDIT: Now that I read your post again, it might be a completely different problem. It's monday morning, and my brain's still asleep I guess.

Quoting: ExpalphalogComputer was running fine last night. Did not download anything or change any settings.

This morning, when I log in my desktop background appears for a split second and then vanishes along with the taskbar. My icons are all still there. Any clues?

I don't know but it sounds like a mint/cinnamon bug.

Try a different DE if you can. Can you install MATE and reboot and log in to MATE and see if you have the same issue ?
Maybe a Cinnamon bug you did not encounter until now.

Which distro are you using? Based on your icon I'd say Mint, but what version? and Cinnamon or Mate? What vid card and driver?

Make sure you have free space in your home directory...

Quoting: stretch611Which distro are you using? Based on your icon I'd say Mint, but what version? and Cinnamon or Mate? What vid card and driver?

Click the "View PC info" link under his avatar for answers to most of your questions.