Hi my name is Shaw aka Dr.Fix-It , Your online expert ready to assist you... It sounds like your ereader had a software glitch, I would suggest to factory reset it and then re-register it to your account to restore normal access. If need further assistance please tell me the exact model ereader / tablet you have?
I.e. Is this a Kindle, Nook, Sony, Kobo, iPad, and which model such as touch, color, paperwhite, HD, classic or basic?
click the link below to see how Kindle Touch looks like, should have it's logo and name on the back:
It does has 4 lines on the bottom and if is a Kindle Touch, from the device:
Once have it deregistered will restart and can next re-register it to your Amazon account to restore all your books on the CLOUD. Can then select your books from the CLOUD to load back on the DEVICE tab section.
Please give it a try and let me know if have any questions along the way with a reply....only rate my answer ok, great, or EXCELLENT after we have worked on the issue together to your satisfaction. Bonuses are welcomed & appreciated. I look forward to any future inquires as well, Thank You