Hi,
sometimes everything freezes: my keyboard, mouse, soft keys doesn't respond. Screen looks like locked, everything looks fine, but i nothing can't do with my PC. I have to restart, and then works all fine.
From where is this error? How can i fix it?

I'm using gnome + compiz fusion, Ubuntu Hardy Heron, and asus X50M laptop.

Thanks for help, and sorry for my bad English...