I agree with craig, because after reading your logline I still have no idea whether this is a horror movie (Like Friday the Thirteenth), or an action movie (Like Die Hard)

That will come from describing the bad guy, is he a serial killer a robber? a stressed out employee? Are they being held hostage? Are they just in the wrong place at the wrong time?

Here would be an example of a logline with more specifics:
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“When a crazed killer shuts down the power, a failed engineering student must rally his stoner friends to help him get the high rise elevators working to escape the madman”
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Of course yours would be different but as you can see in my example by describing the ‘culprit’ as a crazed killer, we now know what genre’ the movie is.