video play back problems-video will play and then starts to hesitate or freeze for a second. Sound is fine, video hesitates in play back

I updated my system from 10.04 to 12.04. My video play back in the first system was perfect, no problems. In the new system, I seem to be having some problems. Sometimes when I turn on the computer, the video will play all the way through with no problems. But if I select a new video after the first one has finished, the video hesitates through the play back. The sound is fine but video will freeze then play, freeze, then play and it will do this through the entire movie.
Other times, I will start a movie and it may play fine for the first 15 minutes or os and then start freezing as described above. Then other times the movie starts freezing from the start.
It does it in every movie player I down load and play it in, vlc, movie player, moovidia, etc. It is the same in all of them.
I downloaded the css and most of the other things I have read about on the interntet for movie play back but it is not helping. I am just wondering if I have the wrong gstreamers selected in the synaptic package or what.

I would appreciate help from anyone who has an idea how to fix this.
Thank you.