Mozilla Thunderbirds- Virgin media (UK)..password did not succeed

Hello I use Thunderbirds on my PC. I use Virgin media (UK) as my provider. Recently Virgin have started to force customers to include/use alternative emails and servers and I now am having to use a G mail email address, in conjunction with my virginmedia address. I'm a little confused by it all. My current problem is. Mozilla Thunderbirds can send emails, but can't receive them. When I check the virgin website and emails, they are sending and receiving, but they are not arriving at Mozilla Thunderbirds. So the problem is with the settings on Thinderbirds. I think My error messages are. "Sending of password for user @~#@virginmedia.com did not succeed. Mail server pop3.virginmedia.com responded: [AUTH] Authentication failed. I re-enter a password then get "Login to server pop3.virginmedia.com with username @~#@virginmedia.com failed" In put please. Robbo