Try trashing the prefs.
Also, when you say you updated the driver - does that mean the graphics driver? If not, go to the nvidia site and grab the latest version.
turn off virus software if you're using and try again.
Thanks for the reply. I have updated the graphics driver on Nvidia website as well.It still does not work.
Under project settings: Video rendering and playback, i have both mercury playback engine GPU accelerator and mercury playback engine softway only. it is currently set as mercury playback engine GPU accelerator.
Thanks in advance
Okay, try disabling the mercury playback engine to software only and if try again. if that doesn't work, try an uninstall/reinstall.
What are the specs of your media?
Also, if you don't absolutely need QuickTime, try getting rid of it.