Reset procedure for DX is now different -- requires two steps
I just encountered this problem on my DX and there is a new reset procedure, according to Kindle tech support. A software upgrade apparently added a step, probably to prevent accidental resets. The new procedure is to slide the power button to its on position and hod it there for thirty full seconds, then release it and press and hold the HOME button until the screen flashes.
I had tried the old 15-second power switch procedure to no avail, then called Amazon via their web CallBack link. They called back immediately and then walked me through this process. I asked about the 15-seond method still published on the Amazon site, and they said "that's out of date since the most recent software update." I didn't even know there had been an update! Apparently Amazon can install these unilaterally and silently when it wants to.