I have been an active Vegas user since 2011 and I have never encountered a problem like this.
Last month, I got a new laptop and I installed Vegas onto it. Problem is, mp3 would load as one large glitch and MOV files wouldn't open either. The MOV files would attempt to open, but just cause the project to crash, making it impossible to open old projects. I have QuickTime 7 installed.
The strange thing is that I tried opening mp3 files and MOV files in 13 and the trial version of 16, and there were no problems to be found there. I have hundreds of unfinished projects for work that I can't afford to lose by switching to 13 (which doesn't open projects from 14) and I don't have the money to upgrade to 16 right now.