Thunderbird email not working on my main email account

Hi, I live in the UK and my main thunderbird email does not send emails ...i can recieve them....i use virgin media as my ISP and i have checked that my email works on their Web based email & it works fine. Summary :- I have 2 email addresses, ,,,,,my main account does not send. i have another account and it works fine .. i entered a new password in the second account , saved the new password in password manager for the 2nd account ..All good with that . There is NO saved password for my main account as i removed it thinking it would cure the issue ...err No it did'nt . When i open Thunderbird on my main email , it asks for a password ...now being as i removed the password requirement ...is this a contributing factor ....... Any help would be greatly appreciated Kindest regards Derrick