Weights and Bias set to NaN
I think there is some NaN values in your data set.

First time it is printing the random values which are generated for the weights.  But after first step, that means, after the first update of weights, they are becoming NaN. That means there is some NaN values or some missing data in the training data. 

Check your training data. I am not clear how tensorflow handles the NaN or missing data.