A dew questions. What are your current system specifications and also what programs are you using to burn the movies??
is it possible that your heat protection is kicking in, and shutting your system down? Feel the back of your PC and feel if it is hot or not. The reason I say this is, my computer did the same thing, but everytime I ran the CD ROM it restarted. Turned out my power supply fan was burned out, and the cd starting up was just enough heat to trigger the shutdown protection.
