When I tried to install Technical Preview of Windows 10 on my Nokia Lumia 820, I ended up with phone which went into infinite loop of updating.

As a result of that phone became unusable and there was no way to bring it back to life without any additional intervention.

To get phone back to life I used fostware available for free from Microsoft:

…and here is how that went…

On first screen I had to indicate that my phone does not startup or respond otherwise phone was not detected by computer at all.

 

Software advised to disconnect all phones and then continue, which I did.

On another screen software was waiting for the phone to report to operating system.

Same time, when my Lumia 820 was booting up and software did manage to detect the phone I got NOKIA logo on mobile screen.

Once phone was recognized by the software I got information about available version of software and question if I want to download it.

There is no software images for Lumia distributed with the application. All images have to be downloaded on-demand once model of the mobile is detected.

So, Lumia software image download is started and in about half an hour I will have it ready to install.

Once installation started I got red background on the phone with NOKIA logo and progress bar.

Also, in the application I could see progress bar while OS installation was in progress.

Once OS installation finished, phone restarted and application was waiting for the phone to come back.

After restart phone was successfully recognized again and I was informed that phone software has been successfully installed and user content erased.

Now the phone is fully operational and Lumia Software Recovery Tool recognizes it properly and showing available version of software, which I can install on the phone.

Hope that helps to recover Lumia 820 or other models while phone will get screwed by some Technical Preview software 🙂