You can now use official Nokia Software recovery tool, in case you face issues with software or software updates. If your phone is not responding, it appears to be stuck or is not starting you can try to recover it at home by using this recovery tool.
There is risk however with use of NSU and one can loose warranty if the firmware is still unapproved by country or if anything like power, connection etc go wrong you can brick your phone. So, do it at your own risk :P.
In case if you want to know suitable firmware for your device click here to check the Lumia product code related firmware list.
For downloading the NSU retail 4.1.0, click here.