This is what I see when I go to the site instead of the header - has been like this since yesterday

Try forcing a refresh using CTRL+F5.

Yay - thank you Joshua! It worked. I have never had that happen and it was making the site unusable.

I've had it very occasionally happen with different sites. Something doesn't load correctly the first time and the browser doesn't realise it failed, so it caches the corrupted data instead. Easiest way to fix that is to force a refresh of the page.