When it freezes, can you press control-alt-f1 and get to a text terminal? After that, if you press Ctrl-alt-f7 (could also be f8), do you get back to the graphical environment, and does it work again?
When it freezes, can you press control-alt-f1 and get to a text terminal? After that, if you press Ctrl-alt-f7 (could also be f8), do you get back to the graphical environment, and does it work again?