AFAIK Mint 13 is rather old, version 14 is already released, so unless you're upgrading regularly, your software (including Cinnamon desktop environment and Nouveau graphics driver, any of those can cause messed up display) may be outdated, and the black bar bug may be already fixed.
A quick advice would be: switch to a text console using Alt-Fn (Alt-F1, Alt-F2, etc), log in using your name and password and do the following:
sudo apt-get update && sudo apt-get upgrade
Type your password again when sudo asks for a password, then say yes when apt-get upgrade asks if you want to download updates.
After that, press Ctrl+D to log out, then Alt-Ctrl-Delete to reboot. Please post the results here.