If your Nokia wouldn’t boot up, or if it failed booting up. I remember doing this three hand salute hard reset ,Well, if your Nokia Lumia 800 is not turning on or fails to boot up, you can try performing a button hard reset on your Lumia 800. It will erase everything, but it will hopefully save the phone. Here’s how to do it:
1.The phone should be off. Hold in this order and at the same time the volume down, camera and power buttons.
2.Keep holding the keys for another 5 seconds after you get some kind of response.
3.You are done, hopefully your Lumia is booting up by now.