I was recovering my Lumia 520 using Windows phone recovery tool but suddenly it stopped working.

[WPCentral Question]

And now phone it is not connecting with the PC. I think my phone has lost it's OS. What should i do?

 

[realwarder]

Connect to Lumia Recovery Tool again. Select the option saying phone is not shown.

Press Power AND Down Volume for enough time for the phone to vibrate. It should then be updatable.

(only do this after you are totally sure you are not still mid-firmware update/install from your previous attempt)