What are the other apps that you have installed?
Have you tried simply restarting your MacBook?
Have you tried repairing permissions?
When you try to launch Aperture, do you get an error message? Does anything else happen, such as 'Aperture' showing next to the Apple in the top left corner (indicating that the program is open, with menus, but no document open)
Do you have a problem launching any other apps (such as iDVD, for example)?