need to ask questions...
has this always happened from day one of purchase?
if not, did it happen prior to an install of an app or uninstall?
Do you have an MHL adapter or Media link attached to the phone?
does this happen with a different usb cable?
different computer if plugged into usb port?
if you plug it into the wall does this issue occur?
if you unplug it does it go back to portrait?
does it start in the homescreen? or some other screen?
do you use blinkfeed?
these questions will help get us all on the same page...