Press Play, button turns grey and the game has a think. Then after a short while the Play button turns on/green again.
Basically nothing happens.

Halp!

More Information is needed, this isn't even enough to make a guess :)
System-spec, failure notices?...

Two known problems that can cause something like this are

I.Resolution
If the Resolution set for the Game isn't matching the Resolution set for your system it will cause problems up to "onstartcrashes", freezes, etc....change the settings within the setups of your graphic card, your game settings and/or the KB.ini to match your settings.

II.Memory