Intellisense not working in Visual Studio 2008

My Visual Studio 2008 stopped showing me intellisense the other day, unless I pressed Ctrl + Space. This was quite annoying as it is something I have come to rely on. After checking through all the settings, I stumbled across the "Statement Completion" options in Options -> Text Editor -> All Lanugages, these had all been unchecked, by what or how I don't know. I have now reset these options and Intellisense has returned.