try to update windows media player and divx

try to update window patch

try another player if windows media player don't work don't use it and try somethings else

try the same file in another pc

maybe the file is corrupted, try download it again

try copy the file to a usb drive and take it to another pc and test

reload windows

run norton system works on the hard drive

run a virus and spam scanning to your hard disk

if you are using a toobar (example google too bar or yahoo tool bar) disable it and try your luck if that resolve you problem you know the problem may possible be conflicting something

maybe too much memory resident file is loaded or opened you don't have enough pc memort

this is what I can thing of right now hope it helps