Question about facebook?

[mndpsp1]

So usually when i receive an inbox on facebook it pops up with a little red box with a "1" in it above the inbox sign to let me know i have an unread message.

However since about one week i no longer get this red box and i need to check every time if i have a new message which is kind of annoying as sometimes i will be on doing other things and some one will message me to let me know to call etc. And i only read it thirty mins later seeing as i didnt notice it do to the red box not appearing and my that time its too late!

Can anyone help me on trying to get the red box notification to show up?
(ive already been to account settings/notifications and unticked the box that says "only send important emails" and then ticked the box that says "messages".

Thanks for any help!

Ant.