Game not working in the slightest.

[Challah_Money]

After not playing Portal 2 for a couple of weeks, I want to play it again. As it is launching, I get a message stating "No executable file," and, sure enough, When I check the system files, very few, if all of the files/folders are missing. I have restarted my computer, uninstalled and re-installed Portal 2 and the problem persists. In fact, when I prompt to re-install, The game size is described as incredibly small. What can I do to fix this?
http://imgur.com/JhYkW
http://imgur.com/DpbFX
http://imgur.com/5f6g9