Step 1: Backup all your data
The first step is to backup all your data. I personally use cloud storage with Google but you can also use SkyDrive and other solutions to backup your data.
Step 2: Switch the phone off.
Once again, make sure your phone is off whilst using this method.
Step 3: 3 button reset
Almost all Nokia phones have an infamous 3 finger reset and the Nokia Lumia 800 is no different. Similar to the soft reset above, the hard reset is performed by pressing the Volume Down, Camera and Power buttons. Hold all three buttons down until the phone vibrates then release power button and hold volume down and camera for a further five seconds.
Step 4: Phone is reset!
Success!! Your phone is now reset to factory defaults.
In case you missed that, here’s a quick infographic to explain it.