Hello recently i have some kind of problem my roommate is turning off my pc so frequently i lost most of work i did before. So stick to the point: how to in Windows 8.1 Disable shutdown computer while user is logged in - i exactly mean from lock-screen to not be able to shut down pc while someone is logged in, because it seems to be retarded - i block screen to not lose data, and anyone can come and 2-click shut it down - already lost 2 day project progress because of that crap. Another thing is that pc wakes up randomly without any signal probably, because all possible signals are disabled in device manager (only keyboard left). Stick to that one - pc randomly wakes up and while using "powercfg -lastwake" i got result last wake count - 0.
Here you go for disabling the button at login screen.
In Group Policy, go to Computer Configuration -> Policies -> Windows Settings -> Security Settings -> Local Policies -> Security Options
There is a setting labeled "Shutdown: Allow system to be shut down without having to log on" Set that to "Disabled"
That way, no one can shut it down unless they log on first, but by then they're covered by the group policy that removes the shut down option.