If they are looking at your website but not signing up, then I would look for problems with your website. It may not have a clear conversion channel, or may not instill enough confidence in the visitors.
If you are actually speaking with them in person, and they think its cool but don't sign up. Are you sure you have articulated the value to them? There is a difference between cool and seeing the value and wanting to use it.
You haven't provided a lot of information, so it is hard to offer more ideas. I guess your best option is to ask them? No harm in calling and saying "hey, we did a demo and you seemed to like it, but you haven't signed up. Would you mind providing any feedback why so that we can improve our offering".