There are a few questions about win 8 laptops having sleep problems. Mine is a desktop (so power options with batteries and such don't apply) and also my issue might be different.
My system is only about 6 months old. Pretty much every day now, whether I told the computer to go to sleep myself or just let it fall asleep from idling, I come back hours later and it's completely unresponsive. Sometimes the monitor is blank, but usually it's on, with a frozen image of the lock screen on it. It's weird because the screen will go blank when I put it to sleep, then suddenly come back on again when the system freezes up. I have to hard reboot to get it out of this state.