Software reset will return your device to its default settings. Like a brand new phone, no information or data saved on your device. This procedure will erase all your data save on your phone.
If your Nokia Lumia 800 is frozen, it is recommended to perform the Hard Reset.
You can soft reset your Nokia Lumia in two ways. By accessing it through settings or doing the hard key combination.
Resetting through the settings:
Go to Settings > About > reset your phone.
Hard Key Combination:
Use this option if your device is locked and you don't know the code.
Note: Make sure that your Nokia Lumia is turned off.
Step 1. Press and hold the power key until it vibrates then release.
Step 2. Press and hold the down key volume. If the exclamation mark will be shown on the screen, you can now release the button.
Step 3. You need to input these key combination:
Volume Up > Volume Down > Power > Volume Down.
Your phone will reset and will boot up automatically. This might take a several minutes.