OSS 10, firefox, totem, lockup

Hi, Running 10 ( with regular apt-get update ). Click a link to a .wmv file in firefox, option to open with default Totem comes up. Select yes ( rather than save to disc ), file downloads, totem begins to initialise ( ie a window appears but is blank ), at which point screen goes black and all keyboard and mouse input rejected, necessitating hard reboot ( this machine cannot be ssh'd or telneted into ). Any thoughts of suggestions? TIA F