Yes, I tried doing a factory reset (all my ebooks deleted) and a hard reset by holding the power switch for a long time (you can see the screenshot of one of those resets). I also tried discharging the battery and fully recharging again.
I'm not in US. Amazon offered me to change it, but for a fee of $60... I rather buying a new one.
At the moment I'm open to experimentation, like replacing the firmware or jailbreaking the unit.