my computer is not allowing me to open thunderbird desktop

I need HELP, Google gmail are not allowing me to use my email on thunderbird desktop app, I have been using the thunderbird for many years. Somehow I have allowed Google to take control of my account

Please quote any and all error messages you see, completely, verbatim. Screen shots would be OK.

Normally, Thunderbird has no trouble with Gmail. The most common confusion is when Gmail asks for account credentials, and it's sometimes tricky to get the prompt windows to come up,

Please tell us in detail what the problem is.