What version of Premiere Elements, what computer operating system?
Please see the details in the following thread to determine if it applies to your situation. There it went to the distance between the subject and camera when the portrait oriented video was recorded.
Please consider, and supply more details so that we are in sync with the details.
Are you using windows or mac system?
As you mentioned, it was working fine yesterday.
You can try this again after deleting the Premiere Elements preferences.
Just delete the preferences from -
%AppData%\Roaming\Adobe\Premiere Elements\14.0 folder or rename this folder and try again.