The USB of the Premiere is for Power only. Although you can technically power it from another device's USB power port, it is recommended for the streaming players to be plugged directly into the wall for best power source. Your premiere should have come with a power adapter. (that your USB power cable plugs into). If you do not have this power adapter you can use another 1 amp power adapter (ie. cell phone charger.)
The Roku Premiere (as well as other Roku devices) need power to operate. (the USB power cable). The HDMI cable will only transfer audio/video so the Premiere will not work without power. Once you supply power to the Roku Premiere through the power adapter, it will work with your projector.
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Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941