Internet Explorer Browser Issues on Shop Theme

Ive recently been notified by a browser that, when attempting to add items to his shopping cart using IE, no items are present in the cart, when attempting checkout.
Website – https://www.portablestage.co.uk
It easy to check this out on the above site.
I was unaware of this issue as I use Google Chrome, however, Ive found that its a complete site wide issue, in that, no changes made to the theme are retained either on IE.
Any admin, changes, product changes and so on, do not remain.
Has anyone had this issue? Or cna anyone shed any light why it would only occur when using the IE browser. All other are fine.
Wierd. Please help!!