Presently, I found Syntax highlighting feature was not working on a new PC.
After google and tried, I found there were 2 methods could fix this issue.
Sometimes, users will forget to enable Syntax highlighting feature.
You can enable this feature by enable view->syntax highlighting.
If you had executed it, but it still not works. You can try the Method 2.
I found that you can copy these 2 files(as below) from another PC, which Syntax highlighting working, and replace them to your directory.
In Win 7, these 2 files are under:
In XP, these 2 files are under:
C:\Documents and Settings\user_name\Application Data\EditPlus 3\
Frankly, I don't know why it happend, but I just know that Method 2 working.