First post here as I stumbled across this forum as my Kobo Touch has done exactly the same!
Went to update it last night and everything went blank and nothing since
Search the internet far and wide to find all the possible ways to reset it (combinations using the reset button, home button, power button, computer) and still nothing. Only bit of live is the green button while charging and the blue when it attempts to do something.
I have contacted Kobo by email as mine is 15 months old so out of warranty where I bought it. It's a shame that their own software has bricked their own device! Hopefully Kobo will be able to help me out.