[Windows Phone 8 General] wcomhelp:
Got a Nokia Lumia stuck at cogs, black background Nokia logo, Red background Nokia logo, or lightening bolt and gear or no/blank screen?

This guide will tell you how to fix all of these. Once a step has fixed your problem do not continue!

Abbreviations

NCS = Nokia Care Suite

PST = Product Support Tool

Step 1) CHARGE THE PHONE to 100% battery. This can fix many issues without a need to go further.

Step 2) Press and hold volume down and power until vibration occurs.

Step 3) Still stuck? If you now have a black background Nokia logo OR a blank/no screen WAIT for 10 minutes before trying again.

Step 4) Remove the SD card (if you have one) and try Step 2 again

Warning in the proceeding steps we will be flashing firmware to the phone. This is for experts only! If you have a stuck phone and are not an expert take your phone to a NokiaCareCenter (Europe) or a Microsoft Store (Everywhere else)

Step 5) Download and install Nokia Care Suite (during install deselect “Multi Software Updater” we don’t use it)

Step 6) Download and install Data Package Manager

Step 7) Download UserGroupsConfiguration.cfg

Step 8i) If on a 64-bit machine,

Copy UserGroupsConfiguration.cfg to:

"C:\Program Files (x86)\Nokia\Nokia Care Suite\Data Package Manager\bin"

"C:\Program Files (x86)\Nokia\Nokia Care Suite\Product Support Tool For Store 5.0"

Step 8ii) If on a 32-bit machine,

Copy UserGroupsConfiguration.cfg to:

"C:\Program Files\Nokia\Nokia Care Suite\Data Package Manager\bin"

"C:\Program Files\Nokia\Nokia Care Suite\Product Support Tool For Store 5.0"

Step 9) Find your product type and product code if you don’t know them look them up.

Step 10) Run Nokia Care Suite and double-click on Data Package Manager. A window will pop up called "Login to NOL", click on “Work offline”. A second window will pop up called "Work offline", click on “OK”.

Step 11) Click on File->Work offline, a window will pop up called "Login to NOL" make sure Login group is “Nokia Care servers” Click “OK”

Step 12) Fill in your product type and product code click on “Search” then “Download Select”

Step 13) Close Data Package Manager and double-click on Product Support Tool in NCS

Step 14) A window will pop up called "Login to NOL", click on “Work offline”.

Step 15) Click on File->Preferences and make PST stay offline.

Step 16) Click on File->Open Product

Step 17) Type in your product type (digits behind RM)

Step 18) Programing->Recovery->Start

STEPS 19-21 are very important!! They must be followed to the letter!

Step 19) Turn off the power of your phone. (If you can’t just hold power volume down until vibration occurs)

Step 20) Now plug your phone into your computer and immediately

Step 21) Hold power and volume down until vibration and click “retry” when you see the Nokia logo with black background. The timing is finicky so try a few times before proceeding to the next step. If you get “Rebooting…” you have passed this step.

Step 22) You only need to do this once. Open device manager and verify the driver for your phone is “Nokia Emergency Connectivity” if not use update driver to make it the driver for NOKIA FLASH

Step 23) If you got an error like “Message send failed” Try clicking on “start” if you get the “retry” popup go back to Step 21, however if you get an error after it says “Rebooting…” again, try “start” a few more times before proceeding to the next step.

Step 24) Ok this is a bit tricky: Turn on hidden devices in device manager. Now watch in device manager. To change this driver you must not be getting the “retry” popup anymore. Now right click the USB Phone device that is connected and change the driver to “2014 Nokia USB Connectivity”

Goto Step 23) Everything worked for me from there.

Good Luck! Happy Flashing! :)

Here is a link to a guy who made a more complete tutorial