WMP11 wont play WMV?!?

I have Windows Media Player 11 for Vista and suddenly out of the blue it no longer plays WMV files anymore. I have a virus or worm in my computer but so far I'm not sure if it's what's affected it, since other files that have all the icons turn green with an upside down "U"......but my windows media player is fine, the icon hasn't changed, but it just stopped playing WMV.....it'll play Mp3, AVI, WMA, and Video Clip formats just not WMV. I don't get any error messages. It's int eh play list to show it's there, but the screen is blank with no sound....it just doesn't play....is there any suggestion on how I can fix it. And yes I have tried codecs.....to no avail =(