Is it a DroidBOX device?
If there isn't a button on the system bar that hides it (when you click the button), look in the Settings area. If there is a Display section, click on it and look for an option there.
It can depend on what version of android you are using.
But make sure you are using the default droidbox launcher.
Click settings on that and check the display options.
Certainly android 4.4.2 had an option to display/suppress the status bar.
Please take a photo of your home screen with the droidbox launcher and the system/navigation buttons present and i will do some checking. Only looked at an android 5.1 machine so far and there is no navigation bar function at all