Playing a media file (so far have tried .wmv, .avi and .mp3) causes my system to completely lock up, forces me to do a manual shutdown (holding down power button). The cursor still moves wherever I want, but mouse clicks and keystrokes don't do anything. When trying to play video, I can hear the audio portion even though my system is essentially unresponsive.

What can I do to troubleshoot this? It only started happening a couple weeks ago; everything worked just fine before that.