This is very strange and I have never met this problem before.

I have a new laptop. This is what I have done.
1 Started the system, uninstalled some software I don't want, such as nero syncup, skype and its toolbar, bing bar, office 2010, McAfee.

2 Then I restarted the computer

Now it has a strange behaviour.

When the UAC window pops up or I change the theme of Windows, all the maximized windows are not fit to the full screen any more. I have attached the screen capture.

Note the empty space above the title bar of IE.

Currently, I notice that when I click on the log off windows button, the screen will be back to normal. Then log in, the screen is still norm. But if UAC pops up, the problem happens. Also the desktop icons will move down and be away from the space above the title bar.

Does anyone have any idea what caused this? I have never had this problem before.