I have presented you with one logical workflow to isolate and reveal your problem media event or naughty plugin for inspection by people having more expertise than me. Really sorry if it is inconvenient; it's the best I could come up within the past fifteen years.
"Could be" just another *ts charade (fourth this week), but what would I know?
I certainly hope that someone else "has other thoughts." Otherwise, you are facing the dreaded "Magix Support Ticket," where you will be asked for precisely the same information, as alresdy solicited above by Nick, our lead moderator, not me. Your project file doesn't tell us jack.
Of course, you could upload all your source media and project to a fileshare, and see if someone is willing to do all the work for you, or maybe even pull a rabbit out of a hat.
Maybe temporarily rename the AVI files, (just put an x in front of name) just to eliminate as possibility. Vegas won't find them, tell Vegas to ignore those unfound files, and see if you can load the project. This AVI problem , the aforementioned VST, control / midi devices issues and in addition some Quick Time issues have resulted in those hang up on loading for me, and almost nothing else.
Engaging in guesswork by telepathy or speculation is futile. I know I'm no good at it.
You are more than welcome to devise your own rational troubleshooting workflow if ours seems too cumbersome. When you find the troubled event or plugin, post back with full properties. We can fix some things, but not if we can't see them.
This seems so obvious but did you just reinstall the program (de-install first)? That often fixes mysterious problems. When your computer hangs upon loading files, it is usually saying it can't load that file for any number of reasons, bad or missing codec, maybe the file itself corrupt but do try the obvious, (reinstall) first. Let's see. Perhaps you did that already and I did not see.