It is hard to know why without knowing what kind of system you have, the exact version of AE, if it ever worked, and what changed. No details = no idea what is wrong.
Well im on an windows 7, its weird its started working again but all my adobe products seem to only open when they want too. it usually helps when i restart my computer. I am using creative cloud products might have had a hickup between the change from cs5 to CC. Thanks for your help.