Problem with Windows vista

Hello,
Yesterday, when i started my computer, my theme was windows classic.. I can put the theme windows vista but every time i start my computer, i must change the theme again.. Anyone know what to do ? (I don't want to do a system restauration)

Thanks

(sorry for my bad english, I speak french !

Upgrade to Windows 7.

What neechan said vista is buggy as heck. and a resource hog