If you double-click your Outlook icon and nothing happens, there’s most likely another instance of Outlook running in the background. To remove the other instance, use the Task Manager. Hit Ctrl-Alt-Del. If the Task Manager does not come up automatically, click on the box that says “Task Manager”. Select the second tab, which is marked “Processes”. Next, look for an image name of “OUTLOOK.EXE”. Click on it and hit “End Process”.

Please note that this issue has been fixed in the latest update for Outlook 2003. Get the latest update for Outlook 2003
here.