I got problem playin some of my wmv and avi files.
It starts with a pink screen and then the clip plays in a pinkish background with lines and patches over it.

Open the files with "G-Spot", gives you information about the file and the codec.

Now you see if the needed codec is missing.

Install the codec and the files should work.

I've had a lot of WMV files do this ... and it was because they were corrupt. Updating your codecs is a good idea in case you are using an ancient codec. I'm betting that if it does not happen for more than 3 or 4 movies, the movies are at fault, they are corrupt .