Thunderbird retains the last profile you provided at settings>privacy&security.. But that is probably not current, as you are unable to access the account. My suggestion is to contact your email provider to reset the password.

Ich habe ein neues Windows installiert.Habe mein Passwort vergessen oder es stimmt nicht mehr.

Was this a new computer, or a reinstall of Windows that required reinstalling Thunderbird? More information may help. If you are receiving message that password is wrong, that would indicate that Thunderbird has the old password and it doesn't work.