I know I should not recommend you to do something that risks a total freeze, but if you start beryl again as you did when it froze - see if you can restart x with ctrl+alt+backspace
If so I'm pretty sure you don't have the right driver....
Then install the latest envy follow the instructions in
http://www.linuxmint.com/planet/Alberto ... _available
and install the driver again (automatically I think)