Problems with Mail Program

When I first input my information and email into the mail application, it was working great. Now, I can't even start up the program because it automatically kicks me off. Anyway I can fix this error?

Meaning it just bounces in the Dock a few times and disappears? That's strange. If you still have your install discs, download Pacifist and extract only the Mail.app package so you can re-install it.