The site is actually working but being a bit odd.
Using edge on Windows10 the first time I try https://www.talktalkbusiness.co.uk
it doesn't work and gives a server error
Then I googled talltalkbusiness and tried https://www.talktalkbusiness.co.uk/products
and it works. All areas of the site are OK
After that using https://www.talktalkbusiness.co.uk/
may or may not connect, not sure what is going on there.
I filled in a survey saying their website is playing up and needs looking at.