This has been an ongoing issue with X11 compositers like marco, unity and cinnamon etc... Ifind especially with an Nvidia GPU that as the system runs longer after a number of weeks or a number of months the GUI just gets slower and slower. It's not something you'll instantly notice but just a hint of lag here or there that gets worse.
One hint you'll find is by watching nvidia-smi and checking the utilization you will start seeing random spikes of 80-100% even without maxi........
Uh oh, so you're working on some super l33t code or other stuff that is super important and Linux Mint's MATE or Cinnamon window manager freezes. This means maybe you can move your mouse but you can't click anything, you can't Alt + Tab to another program but everything appears to be working other than that.
The first thing you would do is Ctrl + Alt + F1 (or whatever virtual terminal you want) and get into the Linux bash prompt (the black screen where things really happen :))........
If Linux Mint 17 or other has no window buttons/controls you can do the following from terminal:
marco --replace&
Sometimes it can be fixed if you go to your themes/appearance and choose a new one but in the case like mine where Compiz is installed but not running/working then that fix will not work and will require the marco command above.
What if you can't type in a terminal Window?
If you close........