My Computer keeps crashing while watching mpgs or divx ?

[HopefulDreamer]

My computer only crashes when i'm watching a video in these formats and i try to enlarge the screen by pulling on the corner tabs. Mpg crash while in classic media player so i use core media player and it works fine. But now i'm getting divx crashing on me in media player. Both videos are on different hard drives.
These files have worked all the time until recently. No new updates have been installed.