Incredimail isn't a 'system'. It's a program (referred to an an 'email client'), just like Outlook Express, Outlook, Windows Live Mail and Thunderbird. It's widely reviled and despised by many of the 'regulars' in AB's Technology section because it messes with your computer's registry and frequently causes immense irritation to those people who receive your emails.
Just like Outlook and Outlook Express, Incredimail has a nasty habit of losing account settings. (Which is almost certainly wghat has happened in your case). The easiest way to fix the problem is to completely delete your account and then create it again. (Deleting your account only removes the settings. It doesn't remove any mail from your Inbox or elsewhere). Make sure that you know your username and password for your email account. Then follow these instructions to delete your account
http://help.incredima...x?is=t&article_id=183
and these ones to create it again
http://help.incredima...spx?is=t&article_id=6
Better still, ditch Incredimail and use a decent email client instead.
Chris