I added my categories to my store last night, and everything seemed to be working fine. Then I added just one product so I could do a test purchase.

I'm not sure what I have done wrong but when you click the link in the sidebar or at the top for the product, you get a blank screen. If you click the link for new products, you can see the product OK.
I also get a blank screen when I add the product to my cart or click the go to checkout button.

Can anyone tell me what I've done wrong and how to fix this please?

Here is a link to my store if you want to check out the problem:
http://scrapdragondesigns.co.uk/store/
TIA