Menu ‘Basket’ link broke, ‘Add to Basket’ loads a large black box.

Hi

Overnight we’ve started to notice several issues with the website. Whenever we click on a ‘add to basket’ button, it loads a large black modal box. No notification to say the item has been added to the basket is displayed.

The basket total on the menu bar does show that the item has been added but you can no longer click on this and theres no way of getting to see the basket or even check to complete the order.

Also, products with a variation drop-down list. When you click ‘ choose an option’ a box at the top of the browser (chrome) displays the message: Please select some product options before adding this product to your basket. But we can’t

Our site is essentially broke, one one can complete an order and we’re loosing £1000s by the day. All the plugins are up the date and the theme doesn’t show any update available. Current version I have is: 7.6.0