need help with mac mail

i have not been getting mails on my mac mail 4.5 (version 1084) since the 1st of october 2012. i have not changed any settings except change the password periodically. never had any issues receiving mails before. i have a mac book pro with 10.6.8. whenever i click on "get mail" it shows as if its getting the mails and when its done there is the ting sound that comes as if task is complete, but actually nothing has been downloaded. also i have never been able to send outgoing mails. i know this for a fact as i have been receiving and sending mails from my Blackberry. the email address used is that of my company. please help.