Sony Ericsson C902 - Texts no longer appear as new event?

Hi, I've just recently started experiencing a problem with my Sony Ericsson C902. This happened literally overnight.
Usually when I receive a text a box will appear and it will say New Event and my text will be on the main screen for me to view.
Now, every time I receive a text, the phone still vibrates and makes a noise and the message symbol appears at the top. But, the new event box doesn't come up. This means that I have to then go menu>messages>inbox to find my text.
It's not a massive deal but when you have to do it for every text it gets tedious.
I must have somehow accidentally switched a setting but I can't find it to reverse it!

Jolyon
October 2009