I had a similar problem that I just fixed a few minutes ago: using Chrome on Win7, was unable to get into the forums even after multiple attempts. Confirmed still having issue with Explorer and Firefox, finally discovered I could only get in by changing the format of my screen name and leaving the password blank (I would either get "account not found" or "user name already registered" by using the default). Up until today, I could only access other parts of the site through my account by staying logged in; I would get similiar error messages just trying to log back into the site, and had to use the forgotten password option just to get back in, but that seems to be resolved now.