Media play/pause key not 'caught' by iTunes

I got a new laptop (Asus Q400A, Win8, 64-bit) and installed iTunes. I use it as my primary media player. However, the media play/pause key on my laptop opens the Windows media player, whilst the Previous, Next, and Stop keys all properly work - they skip, rewind, or stop the current track in iTunes. When I hit the play/pause key, the default Windows media player opens.

I've tried setting iTunes as my defualt media player, and have gone so far as to remove the Media Player registries (nothing happens at all when I press the Play/Pause key).

I've also used keybindings on my mouse and headset to send the media play/pause signal, which each have the same effect as the key, so I'm unsure exactly whether the issue lies with iTunes or the OS.