Hi,
Today my Kubuntu 12.04 restart after a crash of my system, and at this time, kate was open. After restartint the PC. Kate lost default highligth syntax. for exemple when i write a javascript code the syntax '<script' is not in black like since or html tag lost its color.
I reinstall kate but nothing change. i purge with apt-get purge kate and reinstall it, i found the solution. i install kwrite which is not on mys computer. But i has also the same behavior. I don't understand.
Can you help me to com back the default highligth syntax ?

Does this work under a new user?
I'm suspecting corruption in your user Kate configuration (which is easy enough to fix if this is the case).

i try it with an other the user but it is the same bug. I put an exemple here. html tag lost its black bold color http://sv.edorh.com/capture.png

The syntax files for highlighting, etc. are provided by 'katepart' and so therefore may not be in the 'kate' package itself. Can you check to see which package provides /usr/share/kde4/apps/katepart/syntax/html.xml and reinstall it?

i have done it since yesterday. i replace my syntax folder with another katepart syntax folder of another distribution of linux. But nothing change

Does this occur with other HTML files?

yes all file lost here hightlight syntax, when i use javascript file for exemple, "<script" tag which will be normaly in black bold is normal. All file i use lost a part of highlight syntax. It is not the file the problem. Kate is the problem, there is a way of remove completely, i use apt-get purge kate, but nothing happened. I very like kate, but if i don't find a solution quickly i will use other editor

Javascript files don't have <script> tags, HTML files do.
In any case, have you tried reinstalling "katepart" (if it is a separate package, it may not be) and "kwrite"?
You might also want to try reinstalling "kdelibs5" and it's associated -data / -doc / etc packages.

As another consideration - have you tried opening other HTML / Javascript files which were not open at the time, and which are located elsewhere on your system?

Maybe you have the wrong highlighting enabled? What does Tools > Highlighting say?