Instrumentation Amplifier Connection Problem
The ground pin on the module is for the bypass caps (as far as I can tell by looking at the board) 

The REF pin is for a voltage offset. For example if you want a 2.5V offset, you could tie the REF pin to 2.5V and the output would be shifted up by 2.5V 

In your application the REF isn't needed (except for the low frequency attenuation circuit) to provide a DC offset because the DC offset is blocked by capacitors upstream.

One thing that might be good to check is the voltages on the AD8221's PCB to make sure they are correct. 

You should be able to power on the AD8221 with the 9V batteries. Check the amplifier to make sure it is working by a circuit like this:







simulate this circuit &ndash; Schematic created using CircuitLab

Move the rail within the input voltage range (output range divided by the gain) with the potentiometer and you should see the output change also. If not then the amp might be broken