No heartbeat packets found

I cant get my pixhawk 2 to connect. Firmware has been installed, reinstalled. Mission Planner, uninstalled, reinstalled. I have tried everything and I cant get the heartbeat packets to connect.

You will need to give a bit more information than that to allow anyone to diagnose what is going wrong.

Com port?
MP version?
Tried different cables?
USB port on PH2?
Ardupilot version?

Is the Pixhawk powered from USB of from the a battery. I find some USBs don’t have enough power to power the pixhawk 2