repeated abandoning nexts
Several things come to mind. Are you finding eggs that are left alone in the boxes and how long between nesting attempts? Bluebirds will have multiple broods each year, probably 3 to 4 in your part of the country. It takes 14 days to incubate and another 18 to 19 days before they fledge and the adults will turn right around and begin the next brood right after that.
You mentioned that you have two nest boxes in your yard and I was wondering how close together they are. Bluebirds won't generally tolerate another bluebird nest within 300 to 400 feet of them. With two nest boxes too close competition may have driven them off. Other things that can cause nest abandonment include weather, predators (especially cats and snakes), human disturbance (but they are actually quite tolerant of humans), even sudden loss of food sources will cause them to just up and quit. There's also the possibility that they just aren't good parents. Young birds sometimes take a while to figure it out.
If you are finding that eggs are being abandoned there may even be the possibility of nest parasites. You may want to clean the nest boxes out and disinfect them with a 3% bleach solution and then leave them open to dry and air out.
Those are the things that just come to mind quickly. Ultimately we often don't know why some birds abandon nests but it happens more often than we realize. Let me know if you have any follow up questions.
Thank you for your response.
Boxes are placed right distances apart.
There have been no predators; I observe boxes daily.
I have cleaned out boxes and found no insects.
Female has never laid eggs in either of the completed nests.
Pair have returned and gone inside each box a few days after completed nest.
Male continues a few days longer.
IIt's about 10 -12 days before they satrt another nest.
If there are no eggs being found I suspect that the female may have a situation where she simply isn't capable of producing eggs - either genetic or dietary.
You may also want to check out the North American Bluebird Society's webpage if you haven't already. I find it to have a lot of very good information on bluebirds.