Items won't go to cart

We've got a problem that has just shown up on our site. No changes have been made to the site recently, apart from a few additional images uploaded using Image Handler.
When you add an item to the cart, you then get a page to say the shopping cart is empty. I've switched off our custom template and checked again and we still have the same problem.
I've also checked this in different browsers just to be sure it wasn't some strange problem with one of them in particular.

Any ideas what may have caused this sudden change in the way the site functions?

URL is https://www.strelitzia.co.uk

Regards
Steve

Santa Square Pants was added to the cart fine for me using FF3. What browser are you using?

The error has been resolved. Most of the problems were caused by our host performing maintenance on the server due to high cpu load...shame they didn't advise us!

Kim..hope you ordered your Santa after you added him to cart!

Regards
Steve