Last year I set up a PM house and two Blue bird houses. In late May we started getting what we thought were Purple Martins. But they really only went in the Blue bird houses. After studing them and some reading we realized they were actually Tree Swallows. We never did see a single Purple Martin all year. This spring I put up the houses and within a week we got a Blue bird couple in one of the BB houses and they are still with us! No Purple Martins though. We bought some decoys and the Dawn Song CD, No Purple Martins . I have kept the PM house clean and free of other birds. Towards the end of June I started giving up. I still kept the house clean and free of other birds but I quit getting up at 4:30 in the morning to go out and play the dawn song. On the evening of July 18th my wife and I were sitting on the patio and I heard Purple Martin sounds. I asked my wife if she was playing the Dawn Song and she said no. We followed the sounds and saw 10 or 15 Purple Martins on the wires across the street. Right away I ran in, got the CD player stretched the cord out in the yard and started playing the Dawn Song. I still play it every evening and morning. Every evening and every morning the Purple Martins fly around our home ( I swear sometimes there are about 100 of them ) fly around the PM house, land on the PM house and leave.
One night 3 of them slept on the PM house porch, the next morning they were still there. About 5:45am they woke up and flew away. They will not go in the PM house for nothing. I'm at a loss. They just keep flying around it and sitting on it for a while ( and thats only while I play the Dawn Song ) and then fly away. There still is at least 100 of them flying around and sitting on the wires and then as quick as they come they dissapear? What is wrong here?
Welcome to the Forum. You may well be on your way to becoming a purple martin landlord.
The martins you are seeing have completed their nesting cycle this season -- they only nest once -- and are attracted to your house as a spot to congregate, but not to nest. Even the nearby wires were probably chose because of proximity to the house.
Some of these late season "visitors" may well remember the site for next season -- when they would be more likely to enter.
Learn all you can by reading here. If you need tips to maximize attactive of your site -- just ask -- and I think there are several Wisconson "mentors" listed with the PMCA as well.
First of all welcome to world of Puple Martining! You will find this forum very useful!
In my opinion (IMO) you are doing nothing wrong. The fact that you see Purple Martins (PMs) and the are landing on your house are the first step in getting them. It took me three years before I got my first couple pairs and I'm in prime PM territory and went through the same flustrations you are feeling now. I had to put up another house to get them due to my location was not the greatest to attract PMs.
You have a great chance to get them next year. Now as John said read all you can and plan ahead. Cause IMO once you get them it's twice as hard to keep them. You should start thinking about Nest competitors if any in you area. They will run off any PMs you might get. The Starling and E. sparrow are the main competitors. Start thinking about what you have to do to deture them.
Next is the ground assult! Snakes, ants, squirrels, Racoons, and then there's the air assult issues,Hawks, facons (not much you can do about these), and owls (some owl guards work). And last but, probably not least is the insect attack.
These are some of the things you can brush up on and be prepared for when you get PMs and odds are you will get them if not next year maybe the next.
No Purple Martins though. We bought some decoys and the Dawn Song CD, No Purple Martins 
. I have kept the PM house clean and free of other birds. Towards the end of June I started giving up. I still kept the house clean and free of other birds but I quit getting up at 4:30 in the morning to go out and play the dawn song. On the evening of July 18th my wife and I were sitting on the patio and I heard Purple Martin sounds. I asked my wife if she was playing the Dawn Song and she said no. We followed the sounds and saw 10 or 15 Purple Martins on the wires across the street. Right away I ran in, got the CD player stretched the cord out in the yard and started playing the Dawn Song. I still play it every evening and morning. Every evening and every morning the Purple Martins fly around our home ( I swear sometimes there are about 100 of them ) fly around the PM house, land on the PM house and leave.