Yeh not very helpful of people to not post how they fixed the problem, i have never done a firmware upgrade on my spark cdm due to reading of others having bricked their units.
Unfortunately i dont have a fix for the bricked hardware but i'd like to say that Arturis support is shit, i have been waiting 3 weeks for a reply about spark crashing Ableton after the recent spark update.
Anyway you would be better asking on other forums ( Maschine forum, gear slutz etc..) that people actually visit and participate in unlike this place which is pretty much dead.
After a bit of googling i came upon this link
http://www.arturia.com/faq/installation/firmware-reset-and-detection-of-a-midi-deviceBut i doubt it will help if your hardware is bricked but have a look anyway you never know with Arturia gear anythings possible.
Tried to find some kind of phone support but Arturia have stated they dont make the number available on the site because they are too small to deal with calls etc.
But they say if you can find the number yourself then they are quite happy to help with support hahaa classic stuff from a company that willing takes your cash but provides ZERO support in return, check the Origin forum, cats paying thousands for a synth and getting squat support in return.
This number i found for Arturia France:
30 Chemin du Vieux Chêne, 38240 Meylan, France
+33 4 38 02 05 55
Ask for Antoine he knows his shit proper, and speaks English.