Px4fmu v2 board can't connect to qgc v3.0

I found a strange problem when i flash program to a new px4fmu v2 board.
The first I connect it to qgc v3.o.
And the qgc note me choose airframe.
So I choose one and reboot it.
But then it doesn’t connect to qgc no matter how many times I reboot it.
Any one occur this ?

Which airframe? It sounds like it’s getting stuck at bootup for some reason.
First thing I’d try is downloading and installing the latest stable QGC (http://qgroundcontrol.com/), reflashing with stable PX4, and selecting a common airframe.

If you’re still stuck you can connect a console (https://dev.px4.io/advanced-system-console.html) to see what’s happening.