That doesn't make much sense. It could mean two things:
1) I go to the Adobe Web site, but I can't download AE! Help!
2) I downloaded AE to my computer, but AI can't open it up! Help!
Which one is it?
If it's the first, your machine probably doesn't meetr the minimum system specs for running AE CC, and it won't let you download it. The solution: get a new machine.
What if it's the second? We'll need more info:
FAQ: What information should I provide when asking a question on this forum?