Help with Visual Styles for Windows XP?

I recently downloaded and installed the patcher and yesterday settled on a theme. It appeared in my drop-down list under properties>appearance>windows and buttons (from the desktop). I was able to choose it and have it work yesterday, I restarted my computer fine and all but when I came back to change my background today the theme dissapeared and went to windows classic theme. Anyone know what went wrong and what I can do to fix it? Thanks.