In my opinion, the client is not invested at this time in learning more about your services (even if it will help them.) There could be many reasons a prospective client is not responding: They are just too busy with their day to day operations, they have been burned before and are jaded now-even though you know your product or service will help them and make them stand out from their competition. They just don't have the money or have committed to other services, ie: advertising and they want to see how that works first.

Their are a myriad of reasons they have not contacted you and you just cannot take it personal. I still try to keep in touch with them emailing, stopping by in person to lend a face to a name or voice on the phone  making them aware of new products and services. After a while, the law of "diminishing returns: will set in. There is an old saying my manager imparted to me. Yes's and No's will make you RICH but maybe's will bankrupt you. At some point you just need to move on.