The yellow light and the double tone both indicate a Pre-Arm Check Failure.
The two most common reasons for this are a bad GPS signal (locked on too few or no satellites or high horizontal dilution of precision) and an interrupted gyro calibration.
Bad GPS signal:
The first time you start up the vehicle at a new location, it may take from 10-15 min to acquire a GPS signal with enough satellites.
Every time we power up the Vehicle, it runs a gyro calibration.
Disconnect the battery from the vehicle and reconnect it to make sure the above criteria is met.
Tones and lights can tell us a lot of different things and can help to quickly identify the current behavior and know what to do to resolve a problem.
Check out this video and check what is the current Pixhawk message
There are also this links that contains other tones:
As the name suggests most probably thing is that the battery is not fully charge and its voltage is below 10.5 volts.
Check out this video for charging the batteries:
This would be one really uncommon issues, due to the fact that the Pixhawk was already tested, and firmware has been already loaded into it.
All we have to do is
If we are lucky enough, we will these tones: Firmware update successful
This is an uncommon issue, but some times the vehicle can get hardly shaken by shipping, or hard landings and the microSD card inside might stop being detected.
When this happens, we need to pull it off and put it back on.
First open up the top shell:
We need to open the Vehicle using the 2 mm Allen Key we sent in the package. Remove only the 3 screws as shown on the pictures below
Once you open the top shell, on the front of the Pixhawk, there's a microSD Card Slot, with the microSD card inserted. Just push and pull off and put it back in. Reconnect the battery.
When everything else fails, you will need to install a ground control on your device for all future calibrations and this current troubleshooting process.
When using Telemetry Radios click on the list of ports available and select the COMxx available, change the Baud Rate to 57600. In case you want to use a USB cable, then the COMxx will change, click on the list of ports available and select the COMxx available and select the Baud Rate: 115200.
Baud rate location:
For Windows 8 and 8.1
Microsoft implemented what is called a ''Driver Signature Enforcement" since Windows Vista, though this is most prominent on Win 8 and 8.1, and will only let you install drivers that are on their database. As most of this software is open source, the drivers will not be listed on their database. You may need to disable that function to correctly install Mission Planner and the Pixhawk (the autopilot) drivers.
For Win 8 follow this steps
For Win 8.1 follow this steps