I found where the problem comes from by chance when I wanted to change my lock screen !!
There is an option to set the "resolution" of Metro UI here :
http://img15.hostingpics.net/pics/311893Capture.png
It was set to "Default" and I set it to "More small"
And now you can see the difference :
Before : http://img15.hostingpics.net/pics/600277Capturedcran20140421072853.png
After : http://img15.hostingpics.net/pics/470546Capturedcran20140421072841.png
There is an option to set the "resolution" of Metro UI here :
http://img15.hostingpics.net/pics/311893Capture.png
It was set to "Default" and I set it to "More small"
And now you can see the difference :
Before : http://img15.hostingpics.net/pics/600277Capturedcran20140421072853.png
After : http://img15.hostingpics.net/pics/470546Capturedcran20140421072841.png
Last edited: