I\'ve copied and pasted the example code from twitter bootstrap to create a basic modal window in my Rails 3.2 app:
Sometimes other css conflicts as well - CSS priority issue.
to check, Go to your modal fade class on browser and then check if there is any custom file comes on top. such as .fade:not(.show)
where it was using its own information not the bootstrap. if you find then you have to change it to your needs .
Hope this helps.