Hi I've simple differential configuration amplifier with ref powered from 1/2VCC VCC is 3.3V. Differential signal is output from AMC1200. When I tried to power it up I have nothing on output.
When you say you have nothing on the output, do you mean that the output is at 0V?
If you haven't tried yet, please disconnect the AD8236 from the AMC1200. Tie both inputs, as well as REF, to Vcc/2. You should read the same (1.65V) at the output.
Separately, with the setup connected, could you probe the inputs of the AD8236 to see what's going into the device?
I apologize for misunderstanding your configuration. It is clearer with your schematic. Yes, I think it would be better to tie the resistors of the high pass filter to mid-supply. The problem looks like it could be the input common-mode going into the inputs of the AD8236, it does not go fully to ground. The AD8226 can sense slightly below ground, and that is probably why the setup is working.
You can also use this design tool to ensure that you operate within the limits of the in amp: