Fans won't just arbitrarily shut down. They generally just fail. Usually, one can hear that coming. I, too, NEVER use sleep mode. I've ALWAYS had problems with it. If you're gonna do anything, just do a shutdown for the night. I have my PC on an uninterruptable power supply just because a brown out killed two of my PCs a few years ago. Nowadays, I just leave my PC on 24/7 unless I get a power outage. Then, I'll just shut down my pc when the UPS gets so low. (5 mins or less remaining)