[Nokia Lumia 920] mariosraptor:
WP8 has different 'service' modes, you will see a big exclamation mark, or a combination of a gear and lightning bolt, then you will need to (remove a battery or) press the Volume Down + Power Key and hold them for about 10-15 seconds.

Answer

If your phone is unresponsive, or it gets stuck showing Nokia logo, then try this: Press and hold both the Volume down and the Power keys for 15 seconds. This should get your phone to restart properly again. If this does not help, then follow next steps to perform OS reset.

Warning: Resetting your phone will return it to the same state it was in the first time you turned it on. All your personal content in the phone, including text messages and apps that you been purchased and downloaded (may be re-downloaded again) will be erased, and the phone will be restore to the factory settings.

Here are two options to follow, depending on whether you can access your phone's settings screen or not.

Option 1: About menu

•Use this option if you can access your phone's settings.

•This option warns about data loss.

On the Start screen, swipe left, select Settings > About > Reset your phone.

Option 2: Hardware key combination

•Use this option if you forget or lose the password.

•Use this option if the phone fails to fully switch on when pressing the power on key.

•Note: No warning about data loss!

Nokia Lumia with Windows Phone 8

Step 1

Make sure the charger is disconnected.

1. Switch the power Off.

2. Press and hold the Volume down and connect the charger, if succeed an exclamation mark (!) is shown on the screen.

Step 2

Then input the keys in the following order:

1. Volume up

2. Volume down

3. Power

4. Volume down

Step 3

The phone will reset and boot up automatically. Please note that this may take several minutes.

Nokia Lumia with Windows Phone 7

Make sure the charger is disconnected.

1. Switch the power Off.

2. Press and hold the Volume down and Camera keys.

3. Press and hold the Power key.

4. When the phone vibrates, release the power key, but continue holding the volume down and camera keys, until the phone reboots.

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How to identify the issue:

After OTA update or ‘reset my phone’ the device can get stuck to ‘spinning gears’.

If 'spinning gears' are on the screen more than 60 minutes then recovery actions are needed.

Repair instruction:

There are two ways to try to recover:

- Two finger reset: power and volume down key until the phone vibrates.

- Lumia 920/920T: Removing the charger and letting the phone battery to run out. Connect charger and wait until the phone boots up.

- Lumia 820: Removing and re-inserting battery

NOTE: In some cases neither of these help, then sw re-flash can be attempted.

---------- Post added at 01:50 PM ---------- Previous post was at 01:49 PM ----------

OR THIS

Affected Products or Services

Lumia 820 (RM-825, RM-824, RM-826), Lumia 620 (RM-846), Lumia 920 (RM-820, RM-821, RM-822)

Introduction

This bulletin gives information for flashing

Bulletin Content

How to identify the issue:

When phone is set to test-mode, battery capasity (state of charge SoC) is written to 0 %. Because of this, in some cases the phone will not start up or if it starts the battery capacity is displayed wrongly.

Repair instruction:

How to Work-a-round the issue:

- Battery removal or 2-finger reset (hold down power and volume down buttons until the phone vibrates) after repair actions will return the correct SoC value

- Phone will automatically get correct value 20 min after start up

- PR2.0 sw will have correction.

NOTE: Flashing the phone will not remove the issue