Pop up alert in To Do

Hi,

When using To Do I don't get a pop-up alert when an item is due to remind me, All I get is a number depending on how many alerts I should have on the to Do ap icon (correct mark) which I might see many hours after the alert was triggered, but nothing pops up to let me know that a reminder I have set it now ready, how do I get the reminder to pop up on the screen?

Thanks,

Noel