How do I select imported data in R?

I need to analyze my data with PCA in R (version 3.3.2) , and the tutorial I have from an older version seems will not apply. I imported the data into .xlsx and according to what I know, I need to select the numeric data for analysis in PCA using the package stats , taking out the rows and columns that name the variables. The commands I had to test are: dadosnumericos <- dados[,3:25] , as an example, and several error messages appear.