Why is the PayPal Checkout page greyed out?

Category Image 006

It seems this fault has been going for years, PayPal don't know why it is and say it's our fault.
I think the checkout page is hosted somewhere else?
My regular customers don't have this problem, it's the NEW customers that can't pay. I suspect PayPal save their details so checkout is faster or pre-filled?
Does anyone have this problem?
Did anyone solve it? Ta everyone, Steve