The only thing you need to do is to re-install the application. Based on what you said, the software still works. Created a copy of the accounts and the database, then re-install the application. You could also try to repair it, but it's not guaranteed that it will work. Additionally, make sure the Windows Update is enabled and all the available updates are applied to the System.
You can find the Live Mail in the Essentials package: http://windows.microsoft.com/en-us/windows/essentials
