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.