have a look in control panel/system & security/Security & Maintenance. Are there any warnings? Have a look in the security section and see if Macafee is showing under firewall & Virus Protection.
Did you look in settings/update & security/Windows defender and see if its on or not. On my PC, I had to turn it on last night to get it to scan occasionally, it isn't meant to come on by itself
However, on another PC here it does start randomly by itself and since we have Eset on machine, having 2 AV running at start up slows PC down to a crawl. Wonder if its a coincidence we used to have Macafee on it as well. Do you have latest version of Macafee?
Are you on the latest build of Win 10? Did you get Anniversary update last month?