when i play a wmv file on any media player sometimes it works ok but most of the times the program sort of blocks and the screen of the player goes totaly green. does this happen to anyone else? does anyone know the solution?
I would - uninstall any codecs you may have installed, uninstall graphics driver, reboot, reinstall graphics driver, reboot, reinstall codecs.
I'm 100% sure you've got a bad WM9 codec Go here. Download it, use it to uninstall your current codec (if it detects that it's installed), then reinstall it.