I wonder how that happens. For those that are confused, typically the name of the program not responding in shown in the top-left corner of this dialog box. In this case, it is Microsoft Windows, although it should be mentioned a non-critical part of Windows is probably not responding hence why you are still able to view this dialog box.
Side note: I wonder how many dotTechies tried to press the End Process button in the above screenshot, by instinct.
[via Sev456 ]