Visual Studio F6 stopped working. It no longer builds the project

I'm using VS2008, been using it for quite some time now, and since I hate using the mouse while developing, I'm always using F6 to build the solution, or Shift+F6 to build the current project. What's weird though is for some strange reason, it simply stopped working over the last few days. In fact, when I pull down the Build menu, next to "Build MyProject" there's no longer a "Shift+F6" shortcut there on the menu?!? Anyone ever experienced this? Is there a setting I need to change?