If your Nokia Lumia 800 start to act crazy, you can always try the easiest fix: restart it. If the problems seems to be permanent, you can use a hidden diagnostic tool that allows you test some of the hardware and software functions of the smartphone.

Of course, this Lumia 800 diagnostic tool will not replace the authorized service repair, but it will give you an idea on the problem, so you can point it out to the folks at service.

By using Nokia Lumia diagnostic tool, you can test the following functions of Lumia 800
Accelerometer
ALS
Audio Loopback
Bluetooth
Camera
Battery Status
DTMF
Hardware Buttons
Headset Detection
LCD White
Lights
Magnetometer
Power Source
Proximity
Speaker
Touch
Vibration

How to access Nokia Lumia diagnostic tool

In order to acess Lumia diagnostic tool, press ##634# in the dealer, and the tool will start. It will also be available in the application list. Remember, this is only available in Nokia Windows Phones, it will not work on other Windows smartphones like Samsung or HTC.