Not entirely sure , what sign in problem you mean but I think you are referring to the Google Account Verification after factory reset on Lenovo TAB-3 7 Essential . To fix this issue you will need to do a "Hard Reset"
Issue is resolved , you may begin your download from the link given above as download servers error is fixed
Hurrah! Done. Its working now. What process worked don't know. Kept trying and finally succeeded.
Your treat is confirmed once again.