google sign in keeps coming up & i can't send or receive mail

Tbird worked fine with my Gmail account until two days ago. From that point it keeps on asking for my gmail password at login, at the two minute refresh for new mail and whenever i click on another folder like sent or trash etc. Email address and password are all filled correctly, I also have a yandex account which still works at the moment. Unfortunately i tried to be clever and delete the account thinking i could just recreate it but then it says " Incoming server already exists " . Please see pics. Please can some Clever person help me get my email working again... Dez