This isn't anything to do with phpBB or you.
If you read the Dreamhost status page comments:
http://tinyurl.com/2yqnh6 scroll to the bottom of page 3 and the top of page 4, you will see this issue is effecting all php based forums & blogs hosted with dreamhost.
Everyone's worked early in the evening and went down at the same time. No one can log in and no one can post. It's been 15 hours now & no response or actual post on the Status page about the issue from dreamhost yet.