I had the same problem for about three months.
I couldn't view any DVD, VCD or any video type format files using the WMP or Tiger Player(WMP Classic) cos it was zoomed.
Some videos could open in Apple Quicktime player but experienced some sound problems. I also tried using anti virus softwares, uninstalling and installing a fresh copy of WMP but the problem remained. At last this is what I figured out!!!
This problem is not a cause of a Virus, Spyware or worm if the problem is not resolved by an antivirus software.
And if it remained in more than one application it shouldn't a problem of an application.
Any Video and audio files we use to play back on a computer uses a device or a computer program capable of encoding and/or decoding a digital data stream or signal, calls a "CODEC".
And it doesn't depend on the software you use. Some video or audio won't be able to playback or may experience some difficulties if the proper codecs are not installed or corrupted.
As I found my problem was with the codec called "ffdshow video decoder". When a video is played a task bar icon could see. So I simply changed the configurations so I could view the video without any difficulties. It was that simple....
So the people who have the same problem.
Your problem should be with the same condition. First try changing the configurations of the codec that your computer use when playing a video file. If it is not worked, try uninstalling and install a fresh copy by downloading it.
(to know more about codecs try google search. and Wikipedia is a good recommendation)
Regards
mAxc