Until a week ago I was happily coding html.erb files in Notepad++ with syntax highlighting. Then my hard drive crashed.
I reinstalled Notepad++ on my new system but when I open my html.erbs, only a few of them are highlighting properly.
I think the problem might be that most of these files are being considered 'normal text files', where the few that are working are considered 'html files'. I tried 'save as' html file of the same name, but it isn't working. How can I get my syntax highlighting back? This is seriously slowing me down.
You could try going to Language > H > Html and that should highlight stuff.
Just in case, if anyone meets my situation: I had activated Enable global foreground color in panel Settings -> Style configurator..., deactivating it reactivated syntax highlighting.
Another possible situation that could cause this is if you install new themes. If the theme doesn't have certain languages defined and you use one of those, then you will lose the syntax highlighting as well.
To Check: Settings -> Style Configurator
Check that the language is there on the left hand side for the current theme you are running.
I had the exact same problem and none of the posted solutions worked for me so I digged deeper and found that I mistakenly assigned my user defined extensions twice under Settings → Style Configurator, for example SQL and XML.
Deleting my user defined extension from one language restored the syntax highlighting.
So I Know this problem was solved 7 years ago but it's the top result on google so I wanted to add what the solution to my problem.
Under Settings -> Preferences... -> Languages
I had stupidly disabled python without realizing that that's what I was doing, just had to put it back into available items.
I had this problem when reinstalling notepad++ because with the new install, .r source code files were being recognized as REBOL instead of R. I had to manually remove the r file extension from the REBOL key in the langs.xml file. For instructions, see the similar question on the Notepad++ community forum at this link.
Go to Settings -> Style configurator... then disable Enable global foreground color and Enable global background color. This fixed my problem.
来源：https://stackoverflow.com/questions/3418191/notepad-not-syntax-highlighting-my-files