You need to give it some AI. You need to make a relative simple script for the box to make it do what you want when you want it to. The simpliest method I guess is to give it a player proximity command in script. i.e. plyrdistwithin=yourdistance.
Then you may need to activate it, if necessary using an object (can be invisible) as a trigger and utilise the activate if used functions of FPSC.
It can be a little tricky if you are new to this, but is not really hard to achieve and the excercise of getting it to work will teach you agreat deal about working with scripts/AI and FPSC. Well worth a little effort.
Study of any FPSC script for a door which opens relative to player proximity will show you how to do this.
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