I had that problem too a few weeks ago. I could log in one day and couldn't log in the next. I had AdBlock Plus on using Chrome and it was messing with the DVC website. Make sure you're accepting cookies and that AdBlock Plus is turned off.
I actually have that problem on one of my computers that I use. It turns out that if I put in my password and then my username it works but I cannot put in my username first, it simply will not let me!