Assuming that you have the pre-requisites installed, was the initial connection to the AF Server successful during the install? PI Web API stores its configuration information in the AF Server, and you need to make sure that the user that runs the install has the required permissions to AF.
If you can share the exact error returned, that may be helpful too.
Could you also let us know if the AF Server is on the same machine as PI Web API? Also, was the installation of PI Web API done with a domain or local user account?
It's been a while since we spoke about this issue but I would like to know if you have found the solution to your problem?
I am marking this question as assumed answered. but do not hesitate to post again on this thread if you need further help.