I had the same issue a little while back. At first the site let me in, but halfway through filling up my cart it locked up. Repeated attempts to get back in failed. Then I tried a second computer and that very same sequence of events happened to that computer. I ended up calling my order in via telephone, but there was nothing saved in my cart to reference so I had to have the nice lady search each item for me. (luckily I had written all of my items down).
I never did figure out why it happened. I'm going to place another order soon, so we'll see how that goes.