NA as p value in R

I am extremely new to R starting from scratch from a non technical background, for my thesis I need to forecast using ARIMA technique. As an initial step I am trying to check the stationarity of my data set using adf test, but the p value shows to be NA and dicky fuller static as NaN, I have imported data from excel in csv form and converted it into data frame in R. Please tell me how to resolve this problem. Thankyou.