There is a known issue that happens to all of us where once per month or so your computer will randomly starts prompting for the Outlook password in the middle of the workday. Outlook will open but will not send/receive emails. When this happens, the fix is not to re-enter the password over and over, that doesn't work. You do not need to reset or change your email password.

The fix is to click on Start - Log Off and when you log back on it will start working again.