nVidia GeForce GO 6400 Jerky Video Playback Vista Ultimate

Hi All,

I have a Sony Vaio VGN-S580 and i upgraded it from XP to Vista
ultimate, it was working great until i had to format the drive and
reinstall everything. I recovered from the recovery CDs upgraded to
Vista Ultimate again but now the interesting thing is that video play
back is gone crazy. When i run any video on the machine the video
like pauses for a fraction of a second every second that for any video
playing even the sample wmv files that comes with vista and also the
small operation avi files when copying deleting files and sometimes
when i play a video Vista just Bluescreen

I tried installing Vista from scratch but still the same problem on
and on.

The Machine is

2.0 Ghz Centerino

1.5 Mgs RAM

nVidia GeForce GO 6400 (Deafault Vista WDDM Driver)

any idea about what the problem might be? oh the only thing that is
changed that my DVD drive is broken and i took it out, not sure if
this would affect anything

your help is really appreciated

Thanks

Mustafa