I have tried 4 times to save the movie with the same results.  It starts to convert the file but stops about 10% into the conversion and shuts down the computer completely.  I tried resetting the time before the hard drive shuts down in the advanced power settings up from 15 minutes to 120 minutes but no change.  I tried burning a DVD but it still shut down.  In each case it leaves a tmp file but will not resume saving so the temp file is useless.  Is this a hardware or software problem?

My movie is all video and lasts about 66 minutes so it is quite large.

Thanks.