Boost won't work after configuration of .HTaccess
You can verify Boost is working by browsing a page as an anonymous user (e.g. using your browser's Incognito/Private Browsing mode) and looking at the source code of the page. If Boost is working you should see a HTML comment at the bottom of the document that looks like this:

&lt;!-- Page cached by Boost @ YYYY-MM-DD HH:MM:SS, expires @ YYYY-MM-DD HH:MM:SS, lifetime X hours --&gt;