I found an interesting discovery with Notepad++ where PHP, HTML, CSS, etc language syntax highlighting didn't appear in the language menu. Not sure if this is the result of the way an older version set the settings--whereas, even if you upgraded to latest version (without uninstalling first), the upgrades wouldn't overwrite the original settings file. I think this was disabled at the time of install when it asks if you want it to be your default for HTML files; where I normally UNselect this, since I use a PHP IDE to handle PHP, HTML, CSS, etc files.
Anyway... The fix:
Go into "Settings" , "Preferences", "Language Menu", then move over the missing languages from the right to left selection pane.
And that should do it. Now you should be able to syntax highlight your file with the previous missing languages.