You have not provided enough information. Your question would be like going to an automotive forum and saying " My car doesn't work, what do I need to fix it?"
(while I am temped to leave it at that so you're left with the "What information do I need to provide" question hanging over your head ... here are a few of the things we need to know ...)
Is there line of sight? Real line-of-sight where you can stand where an antenna would be and see where the antenna would be at the other location.
How much clear space is there, assuming there is a line-of-sight. More than just a little peep space is required.
Imagine an American football with the pointed ends located at each antenna .. depending on the distance, whether there's a span of water in-between, and some other factors, the diameter of the body of the football will be wider or narrower, and within that body is the required space needed to operate the link effectively.
Once you've figured out whether there's line-of-sight, and enough line-of-sight, then you need to look at the weather, and decide what kind of reliability you require.
Then there's things like other systems that might interfere, security, cosmetics, power requirements, antenna requirements, and a large basket of other related questions.
It might be better for you to contact someone locally and have them do the site survey and equipment recommendation. The process can be complicated and (especially if not done well) expensive.
Good Luck
Scott
