To save you pressing CTRL+ALT & DEL and manually closing the process, you can create a batch file using Notepad on the desktop with the following line:-
taskkill /F /IM hl2.exe
Save the text file with the ".bat" extension.
If you want to change the icon, just place the bat file in your gesource folder, create a shortcut and drag it to the desktop. Now right click, select properties and under "shortcut" tab click on "Change Icon", select your "gesource/resources" folder and double click the GES icon, then apply followed by OK.