If you are using a Microsoft Windows computer,
it is critically important that you
display files that are normally hidden from you
by your selecting the 'Folder Options' radio-button
"Show hidden files, folders, and drives".
And it is equally important
that you display all file extensions
that are normally hidden from you,
by your de-selecting the checkbox
"Hide extensions for known file types".
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,
for example, parents whose 2 to 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 display all file extensions.