Site suddenly not working in IE 11

It doesn’t for me, make sure you clear your browser’s cache.

I did clear cache, and also tried from 4 other computers, 2 of which are in different cities. This is what I get in IE 11:
https://screencast.com/t/zFM7wHaTPr

Try deactivating all of your plugins to explore whether any could be responsible. If none are, keep all plugins deactivated and switch to the Twenty Fifteen/ Fourteen theme to see whether it could an issue with your theme.

I deactivated ALL plugins, still had error
I then changed to twenty fifteen theme – no problem loading.
So I guess I need to ask the theme author, right?
Unless there’s something else I can test?
Thanks for your help

The theme authors would be in a better place to debug the issue at least. It’s something to do with the JavaScript running on that page. You could try debugging this by using IE11’s tools: https://msdn.microsoft.com/en-us/library/gg699336(v=vs.85).aspx

See what error message you get