Since nobody wants to reply to my old topic:

My custom themes no longer work. I had the uxtheme.dll installed, and my theme was working fine. I come back a week later, after being on vacation, the theme was reset to the windows classic and I couldn't change to the custom themes anymore. I tried reinstalling the uxtheme.dll multi-patcher, and it still doesn't work.

Start -> Control Panel -> Administrative Tools -> Services -> find "Themes" entry and double click it to open -> Make sure "Startup" is Automatic and "Service status" is Started. If not, do the changes -> Apply and Ok

Also, if you have recently updated your Windows (especially a service pack update) it might have changed the way uxtheme.dll works so you have to make sure you have the proper version of the multi-patcher.

Urgh
I dunno what I did but it magically works now. :S