zoom video suddenly stopped working

Hi I run Windows 10, multiple browsers and the zoom app. I use zoom most days for work. We use company zoom accounts. Today when I logged into an online zoom meeting as host  as I do every day, zoom said the virtual background could not be loaded and the result was my video was turned off by zoom. I had a grey screen with a camera logo with a line through it instead of my camera working as normal. I tried logging in from different browsers, same result except zoom didn't tell me the virtual background couldn't be loaded, it just disabled the camera. I tried different zoom accounts, I tried the zoom app. Same result. I checked the settings for both the app and the online zoom system and both systems had 'none' highlighted for a virtual background. Switched my computer off and on ... no change. Cleared cookies / cache - no joy. I tried zoom for one of the accounts on my iphone using the zoom app and it worked fine. The problem is with my computer. Any ideas?