Option key no longer allows Windows or Mac boot option

Until recently I was able to depress the Option Key at startup to select Windows or Mac OS's. Suddenly this is no longer possible. Holding down the Option key does nothing at all... The Mac simply boots into my OS X install. I can use Prefs > Startup Disc to select the OS I want booting though I would like the ability to choose from a cold boot.

Anyone have suggestions as to why the Option key no longer works as intended or how I can fix the problem? - do I need to re-write a boot file?