Movies i download crash my computer

I have experienced this problem in the last few weeks when i downloaded a couple of movies from most replied threads cos i thought the uploader is trustworthy. So when i play the movie, my computer crashes and i get windows has stopped working error. I have to watch the movie in safe mode and delete from safe mode in order to use my computer normally.
Why is this? All movies i download are 720p.
Answer #1
Did you watch before movies in 720p and it worked?
Answer #2
Do you have the proper codecs? Update your drivers.
Answer #3
Make sure you have all the right codecs.
VLC uses its own, its a damn good player.
I recommend MPC, get it with the K-Lite codec pack.
Also, Make sure your system is up to date and free of viruses.
http://www.codecguide.com/download_k-lite_codec_pack_mega.htm