I bought a used e-ink Kindle Touch (5th gen) from eBay. Arrived in good shape, although the battery was dead. After charging, it booted up fine, but to an obsolete version of firmware: 5.1.2. My first step was to connect it to Wi-Fi. My next step was to try and register the Kindle to my Amazon account. I got this error message repeatedly:
Unable to Connect
There was an error while registering your Kindle. Please try again later.
So I decided to try to update the firmware. That option was greyed out. I was stuck.
At this point, I feared that the unit had been reported stolen, so I called Amazon tech support at (866) 321-8851.
It took an hour, but "Joe" in the Philippines got everything fixed for me. To skip all the blind alleys we pursued, this is what we found:
- 5.1.2 is too old to register with Amazon's servers.
- 5.1.2 is too old to use Amazon's automatic updating service.
So I went to
http://www.amazon.com/gp/help/custom...deId=200790650 and
- Downloaded Software Update 5.3.2.1 and installed it via USB cable.
- Unmounted my Kindle.
- Rebooted my Kindle. (This took a while.)
- Downloaded Software Update 5.3.7.3 and installed it via USB cable.
- Unmounted my Kindle.
- Rebooted my Kindle. (This took even longer.)

At that point, I was able to enter my email address and password to register the Kindle to my Amazon account. It worked, and books began to download.
So, at this point, everything seems to work, and I have a functioning Kindle for a third of the price of a new one.
I hope this post helps someone else in a similar situation.