Hi. First off, if that is the syntax of your .htaccess file, I can see why it doesn't work 😃. Seriously though, the syntax is like this:
AuthUserFile home/YOU/ whatever/yoursafedir/.htpasswd
AuthGroupFile /dev/null
AuthName "please enter your password"
AuthType Basic
<Limit GET POST>
require valid-user
</Limit>
Also, you password holding file IS NOT a.pw, it's .htpasswd.
Another thing. .htaccess and .htpasswd have be in separate directories, and if they are in the same directory, you must still specify iy. Where it say AuthUserFile, YOU MUST PUT IN YOUR COMPLETE UNIX PATH, INCLUDING .HTPASSWD just like I did in the example.
Also, I hope you know that the password in the .htpasswd file has be encrypted. For example, bob:bobby would look like this:
bob:acFt.VFNyGxdo
Hope this helps, good luck.