As the title implies, I've managed to lose syntax highlighting in my parameter window. I'm on windows 7. Basically regardless of what I type, “string”, rand(), etc are all white. I've checked in the preferences and syntax highlighting for all windows is checked on.

Is there any other way to restore this?

From the main menu, open Window > Hscript Textport. From there type: Now quit Houdini, rename that directory to something else and then start Houdini again.