Deploying Windows Phone 8 application on device shows empty screen

Deploying Windows Phone 8 application on device shows empty screen

I created a default template, which has two or three textblocks on the
Main Page, added a button with an event and a textbox just for the sake of
testing, wether deploying an application works or not.
The program starts running on the phone, but shows only a blank screen
with a row of numbers on the side, which doesn't change whatsoever. Since
I used the default template, it should show what is present in the preview
window, shouldn't it? Why can't I see anything on my phone?
Please excuse me if I messed up something really basic, I've never created
a wp app before. My phone is a registered Lumia 720.