Lost Ubuntu Mate desktop (blue screen)

I just tried to boot into my Ubuntu Mate machine after it had been shut down for about 24 hours. On boot I got some popup saying there was some error and I sent the details to the developers. Now it's all just blue screen... How can I get the Ubuntu Mate desktop back?

You have to logout from current GNOME Shell session using top right icon and then login to MATE session from login screen.

If your system were corrupted, you can reinstall whole Ubuntu MATE desktop by opening terminal with Ctrl+Alt+T and executing below commands:

sudo apt-get update
sudo apt-get install --reinstall ubuntu-mate-desktop^

then reboot and select MATE session on login screen.