@gordon-richmond I've moved you to the Pro forum section as you'll more likely to get a response there.

http://www.vegascreativesoftware.info/us/support/form/

I have already been to that page, which forced me into this forum. It also provides a series of answers which are completely irrelevant to the problem. Sorry

Have you tried reinstalling (section 19 here)?

Try either reinstall the driver for your graphic card or go back to an earlier driver

Hi vkmast, I have now done that, thankyou. But it now freezes at "Creating video plug-in factory".
Hi Richard-Marcus. Thankyou for your suggestion. I investigated and found that the video card was old, and while Windows 10 loaded drivers and it worked on everything else, I went back the manufacturers site to find that they dont do drivers for Windows 10. So, I have now invested in a new video card, with the latest drives, designed to support video editing etc. Sadly, it still freezes at the "Creating video plug-in factory" message. This is after following the clean uninstall instructions kindly provided by vkmast. Any other thoughts??

Firstly establish and then update your .DOT Framework?

Would your VEGAS Pro happen to be the "Steam version"? Or have you tried to "Run as Administrator"?

Re Grazie's suggestion: From System requirements: "Microsoft .NET Framework 4.0 (included on application disc) or 4.5."

As it says. Application opens, goes through all the various messages, then freezes at "creating Windows"

I'm having this/same issue on my (still) W7 notebook when I close VPro17 and start it again, it hangs at creating screens. When I close down my notebook and start it again, than VegasPro17 starts normally for one time.

When Vpro17 stops at creating (third party) video plugins, normally a reset helps, means start Vegas while keep Shift+Ctrl pressed and clear cached data.

Hi 3Point - This is a fresh install which never gets to run. But I did try your suggestion. No Change. Worth a try though, thankyou.

Hi vkmast - its a full version (700meg) not a streaming version. I did try "run as administrator" no change

Hi Grazie - I tried downloading a fresh version of .net 4.0 SP1. However, when I run it I get a message saying ".net framework 4 is already part of this operating system. you do not need to install ..."

Not having much luck it seems

Actually I asked if it was the Steam version.

And would this thread be of any help?