If you are using Windows,
it is important that you
set Windows to display hidden files.
And it is even more important
that you display all file extensions.
By default, Windows hides certain files
that it has classified as worthy of being 'hidden'.
And, by default, Windows does not display
certain file extensions.
I have no doubt that MicroSoft did this
to reduce the burden upon
their telephone support department
by reducing the number of calls
from parents whose 2- and 3-year-olds
play 'drums' on the keyboard.
This is, however,
a completely unacceptable situation
for you as you work on your Drupal site,
and you should adjust Windows
to display all files,
and all file extensions.