PS: In NHUSD at the K-5 level, you have to be in a "staff" account to use mirroring.
Here is a tip from Stephen Politzer:
There are two types of HDMI to VGA adapters: passive (no power boost) and active (USB power boost). The adapter you tried is passive. I had an active one at some point but can't find it. What it does is connect the HDMI and VGA AND adds an additional USB power cable to provide more power to the adapter. I suggest trying one of these.