You don't happen to have any security / disk cleanse program to clean up your playlist = recent files at start up? "Scan at start up", that is?
Check settings, perhaps take off your security programs, restart, check that they aren't running, play something or two you feel is secure, restart, and check. If you have Windows 7 updates up to date, you can spend an hour or two, without hazard. If you have the material on your own disk, you can disable Internet, by unplugging, that way you should be [almost] 100% sure. Wouldn't really recommend YouTube or others, but you're safe for a while.
BUT JUST try this, remember to get security back on!
And like whs notes, get rid of codec packs. Never have more than one codec pack installed. Uninstall all, and take a look at how WMP works, you can even try "Repair your computer" with the installation disc.
In fact, not having anything financial involved here, PowerDVD is a good buy. It comes with a cost, but their support is tremendous. Sometimes you have to pay for it...