MovieMaker doesn’t open YouTube sign in page

Hi  I'm having trouble uploading to YouTube direct from MovieMaker. I have no problem uploading direct from Youtube. 

When I click on YouTube in Moviemaker it no longer comes up with a sign in page for YouTube  and ask you for your name and password (like it has done for the last couple of years). I just get a message to say "Your movie. MP4 wasn't published. Please sign in again with your email address and password". But, there is no dialogue box to enable you to sign in for YouTube - like there used to be. I get the sign in message if I click on Vimeo - but not when I click on YouTube. Has anyone else had this problem and if so, what is the solution? In Google I have the "Less secure apps" enabled.  I have been using Moviemaker for several years to upload videos directly to YouTube and I have never had any problems - but something has happened in the last couple of weeks and now I can't. 

I don't know why Moviemaker doesn't give me a YouTube sign in page anymore. I tried this on my other computer where I recently also installed MovieMaker and it all seems to work fine. When I click on the YouTube icon I get a sign in message and I can then upload direct to YouTube. But I don't get the sign in message on my main computer anymore - so I can't sign in to YouTube.

Does anyone know what the problme may be or what the solution may be? Is it possible to remove MovieMaker and reinstall it? If so, will that help? Should I restore my computer to an earlier time. I'm getting completely frustrated not knowing what has happened or how to fix it.

Thanks