No longer able to see any windows for Apple Mail
Mail appears to load (icon in Dock & after restart availability of Mail pull down menus at top of screen) but none of the windows actually opens making it impossible to access new mail or any other options from pull down menus. Restart and repairing permissions has had no effect. If the program file has become corrupted how can I download a new version of the program to replace it?
Thank you
iMac (27-inch Late 2009), OS X El Capitan (10.11), 12GB ram