Apple's "Mail" does not show when opened I just upgraded to Yosemite and opened my "Mail" programme, and at first everything worked fine but when i closed it and wanted to open it again at a later time the app tells me its open (by showing me the nr. of unread emails and via a small dot beneath the app sign) but it wont show me the inbox..

can someone tell me what happened and/or how i can fix this?

thanks.
This is standard OS X behaviour for apps that can have multiple windows.

Close (by red button or the File->Close menu) closes the front window but leaves the app running. You can still switch to the app. To open a window do File->New Viewer Window or File-> New Message.

To stop the app you need to chose Mail->Quit Mail