Downloaded files not playing

Starting last week everytime I tried to play a finished movie file or one that had already been on my computer for a while it would shut down the media player with or without notice (depending on the player I was trying to use) and within about thirty seconds. If I remove all the files I had just downloaded, though, everything would work fine. I have tried this a few different torrents (ones from people I have used before) and the same thing happens. I have run spyware, adware and virus scnning programs and have turned up nothing so I have no idea why my files have decided to go all wonky now.

What kinds of files were they? Which players were you using? What have you tried so far for this? What error messages are you getting when you get any? What does your system event viewer show in the way of any errors?

They were .avi files. I tried VLC, WMP, WMP classic, nero showtime. I have tried running adware, spyware, and virus detecting programs, I have installed a newer version of bitcomet, I have tried closing bitcomet and then playing the files. When I tried using any other program besides VLC I got the error message of “This program has encountered and error and needs to close” and i am not sure what you mean by system event viewer.