I was in a similar predicament. I did all the troubleshooting listed in the other posts, and then contacted Kobo Support.
They had me run through the steps again, and then advised me that I would need a replacement device shipped.
The process was fairly streamlined - it did take about a week to get my replacement, but it was brand new, in the box. I've since sent my defective Kobo Touch back, and I couldn't be happier.