PC does not recognize PX4 when I connect it using the USB port

I have a Pixhawk Pro 2.4.8 (PX4). When I connect power, it seems to boot up (the LEDs flash and blink). I then connect it to a Win7 computer with Mission Planner installed. When I connect it, nothing happens. The computer does not detect a new piece of hardware. If I start Mission Planner, it does not see the board.

Where does one get the drivers for the latest Pixhawks coming from China?

The issue is with Missionplanner and Win7.
You need to manually uninstall existing drivers, and reinstall new ones from where you downloaded Missionplanner.
There are threads on other forums about this, but not really relevant here.