1] Try lowering video acceleration under the Performance tab in Tools > Options in WMP.

If that doesn't work, try;

2] Downloading wmv codecs from Microsoft;
Select "Codec installation package" from the "Select download" pull down list.

or download and install the free DivX player from http://www.divx.com

This will install a different player and a codec pack that includes wmv codecs

See if any of that helps.