A few things you can try:
Copy the VOBs to your hard drive. Don't try to edit off a DVD.
Transcode the VOB to another format in MPEG Streamclip or Handbrake.
It is likely that the first VOB has some navigation, and maybe Menus in it, and is not 100% DVD-compliant. That is common with some authoring software, and especially from DVR's. This ARTICLE goes into more detail.
I agree with Jim, that ripping the VOB is probably the best workflow, as it will get past the navigation and Menus to the MPEG-2 file inside the VOB.
Check out the screencast link please Video showed up and played just fine in screen once it was rendered got the yollow box--Why
You need to wait untill the conforming has completed. Right bottom corner; the blue bar.
Don't edit before everything is conformed.
And make sure your video is on another physical drive instead of the C drive.