Sounds like your Compiz and/or Unity settings are screwed up.
Try the following. First of all, since you can't fire up a terminal when in X, switch to non-graphical mode:
Hit Ctrl+Alt+F1. This will get you to the non-graphical mode.
Login there with your username and password.
Now from here, we'll try to reset your faulty configuration.
Option 1: Reset Compiz configuration
To reset only the Compiz settings, execute the following commands:
DISPLAY=:0.0 dconf reset -f /org/compiz
rm -r ~/.compiz* ~/.config/compiz*
This should restore your Compiz settings to default.
Finally, restart X (i.e., the graphical mode):
sudo service lightdm restart
Option 2: Reset Unity configuration
If the above doesn't solve your problem, try yo completely reset your Unity configuration. From this answer, you can use the
unity-tweak-tool for this. You'll have to install it first:
sudo apt-get install unity-tweak-tool
Then, execute the following command:
DISPLAY=:0.0 unity-tweak-tool --reset-unity
Finally, switch back to X by hitting Ctrl+Alt+F7.
Hopefully, one of these will fix it.