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
Stop horsing around 
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.
You probably guessed it right.They might be unable to open the website due to sever connectivity issues as the Ddos continues to overload the server.I'm surprised cloudflaire isn't helping much.Not sure if theymos is using a Load balancer.Forum still loads very slow for me and takes a few seconds to open threads with substantial amount of content.