Farm Bureau Home Insurance review: won't pay on a claim

I bought my house in 2010. I had my home inspection and my insurance company did their inspection. Now my floors are falling in
and my walls are cracking! I put in a claim with my insurance company. they sent somebody out here. Then I get a letter from them saying they won't pay because it was pre-existing! Well, I didn't know what was happening, my inspection didn't show anything. So now what do I do?