Seems like the site is yet again experiencing a DDOS attack. Difficulties accessing the site are to be expected - not much you can do here. The forum, while stable, drags like a dying horse on my end. didn't realise this was a pun until I finished writing it out

If it's not that (e.g. user / account related access), then provide more information since "user can't access to bitcoin forum" isn't exactly helpful in pinpointing account issues.