Just wanted to share my experience.
1.  My PC kept changing my power options (power plan) settings from "Monitor - Never Sleep" to "Monitor - 15 Minutes"
2.  I searched the net and a lot of complaints about this but nothing would work.  I did everything - reset settings, saved, created a new scheme, etc.
3.  I remembered - I didn't have this problem until I upgraded from BitDefender 2014 to 2015.
3.  I noticed that I was running (BitDefender) on AUTO and noticed it was in GAME Mode (have no games - tooooo old for that stuff!).  Now, I don't remember if I always ran in AUTO...
4.  I changed setting to STANDARD - guess what?  Yuppa - my Power Settings now hold "Monitor - Never Sleep" 
It might just be a coincidence - but figured I would share it with the community. 
And no - I didn't change it back to AUTO to see if the problem surfaced again - I don't want to risk it! 