For a while my computer would power down and then immediately power back up, over and over again. The issue is that computers are always sleeping with one eye open, so to speak, and there are any number of things that can trigger a power-up. In my case, I disabled wake-on-LAN, and it solved my problem.
…Aaaand my system failed to suspend last night. I did the “powercfg -requests” thing, and it reported that Firefox was busy playing audio. It wasn’t. I restarted the browser and the operation went away. 
But was there a tab open that could have played audio or video? Restarting Firefox would close that.
Also, have you done any malware and adware scans?