Hello, I haven't run Vegas for several months (2-4) and now when I try to start Vegas it doesn't start and I'm stuck at the "creating video plug-in factory" startup menu, I deleted Vegas and reinstalled it but it didn't help.
Do you have any 3rd party video plugins installed on your computer? If yes, which ones and are they definitely compatible with Vegas Pro according to their manufacturer?
In any event, you could try resetting Vegas Pro back to its default (factory) settings as per the procedure outlined in https://www.vegascreativesoftware.info/us/forum/faq-how-can-i-reset-vegas-pro-to-default-settings--104646/
Also, if it is stuck trying to load a video plugin, go to this location on your hard drive, C:\Program Files\Common Files\OFX\Plugins, create a folder on your desktop named OFX Plugins, and move all the folders from the location there. Start Vegas Pro again, and it should start right up.
Then, open both locations (desktop and Plugins), and move the folders over one at a time. Restart Vegas each time, until it gets stuck loading video plugins. Then you know which particular plugin is causing the issue.