FC2 goes into Sleep/Standby and can't wake up

[knoppix]

I've noticed the last two nights I've left my FC2 on for about 24hrs, when I come back the screen is black and I don't get any response from moving the mouse or from hitting the keys on the keyboard (I've tried all keys to try and wake it up) but no luck. What I've done to wake it up is Ctl-Alt-Del and reboot. I've checked my screensaver under the power saving button but it seems to be disabled. Is there a special key stroke I need to know of to wake my machine back up without having to reboot?

Thank you