After jailbreak, I can not registering amz account

Hello,

I just took a Kindle gen 1 from my room-mate, and jailbreak it

I downgrade from 5.6.1.1 to 5.3.3 and jailbreak like instruction, installed KoReader

everything was great until I realized that I can not de-registering my amz account (Unable to Connect) and "Update your Kindle" in grey-out.
P/S: I need this because "Send to Kindle" feature doesn't work.

I try everything including "Reset Device" and Now I can not register my amz to Kindle.

Can you help me? :(
Thanks