Well all like to play pranks , and this one is the latest in Windows Pranks. This ones a cool one to try on your friends, especially when your friends don’t know how to get it back to the normal.
The shortcut for executing this trick is described below :
for normal windows : Ctrl + Alt + <Up arrow>
For 180 deg it is : Ctrl + Alt + <Down arrow>
However you should know that these are default shortcuts for Intel Extreme Graphics Controller, and you can change them at anytime. To check / change or disable these features goto your windows Control Panel > Intel Extreme Graphics > Hot Keys.