Hi, your copter version is really old 
You should update to the latest stable copter which right now is 4.0.0.
Your Pixhawk1 is still supported and mission planner should be able to detect it and offer the correct version.
I’ve never done an upgrade from 3.4.x to 4.0.x but I’d guess you’ll need to carefully review your parameters after the upgrade.
Edit: There’s a critical bug in copter 4.0.0 so you better upgrade to Copter-4.0.1-rc2 which includes the critical fix