Screengrab very useful.
Timeline would normally show images from video (I'm assuming you haven't filmed 1minute 20 of purest red)
If it happens with all video file types, head on over to Sony Creative Software support - they may have a solution or most likely send you details for a COMPLETE uninstall and reinstall.
If only certain types of video, you have a codec problem. Search the "Sony Vegas" forum on this site for "codec" for some suggestions.

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Tim