When I place an mov file on the timeline, the audio always plays, but the video is black. It seems if I minimize the program and re expand it, the video is there, but may not be for other mov files on the timeline. I'm in Vegas Pro 12 build 770.
I am more conservative than Mike, I have 7.6.2 (also called 7.60.2) on my system and it works fine. If you decide to go for 7.6.2, make sure you don't get 7.62.
I had 7.62 on my system. Someone gave me iphone 5 files. They imported fine, but rendered to audio only, video was black when I pulled the mpg2s that were made from them into DVDA.