I've got the opposite problem of a system not going to sleep: my desktop pc is going to sleep while I'm using it. Playing a game, watching Netflix, browsing the web and suddenly the system goes into hibernation.
The eventlog says the cause is the battery. I do have a UPS battery connected but I'm pretty sure the system was not running from the battery. I've never had this problem with Windows 7 and 8 but since I upgraded to Windows 10 this hibernation event occurs a couple times a week.