If you are using the AOL browser please refer to the "Can I use the AOL browser to run courses?" topic.
If you are not using the AOL browser then the problem is most likely that you have a popup blocker enabled on your computer. Many firewall programs today have popup blockers built in to them. You will need to disable the popup blocker to be able to take our courses. Popup blocker programs prevent popup ads; however, these programs also prevent legitimate programs from launching as well. Check your specific popup blocking program for directions on turning this feature off.
It is also possible that you accidentally moved another window to the foreground, obscuring the course window. Check your computer's task list to find a window titled "Course Window".