What do you mean, only 3 have worked? Do you mean only 3 have appeared in the aircraft menu, or they don't load, or they cause problems? Did you manually load the aircraft or were they installed though an installer?
If they don't appear, check that they are installed properly. Open the FS9 folder, then open the aircraft folder, then look to see if the aircraft are in that folder, if they are not there, then they can't work. If they are there, open the folder of the 'missing' aircraft and check that there are at least 6 folders in the aircraft file, they should be Model, Panel, Sound, Texture and an air file. If either of the last two are misssing, the plane won't appear.