I presume you have ad-ware http://www.lavasoftusa.com/software/adaware/ & Search & Destroy http://www.safer-networking.org/en/mirrors/index.html & as well as a decent anti-virus app.

Might be worth finding out if you've picked up some nasties from somewhere. wma & wmv are easily corrupted files due to their drm which can incorporate links to sites, advertising, & even viruses. The other alternative is a document you've downlded from somewhere Or a site you've visited.