Freezing after Idle

Hey guys, my macbook sometimes freezes up after being left idle for a little while. I cant get the trackpad to respond and none of the keys snap it out of this "frozen" state. Any idea of how to fix this, the only way to fix it has been to force shut down.

is it asleep? how long has it been idle?

No, the screen is just dim I have left it idle for about an hour.

have u tried turning off the "automatically dim display" option under energy saver?