(edit) please can someone delete this? It appears to be a database issue. (for some strange reason the database user has disappeared...)
If you search for "something has gone wrong", you'll find numerous posts: http://vanillaforums.org/search?adv=&search=something+has+gone+wrong&title=&author=&cat=all&tags=&discussion_d=1&discussion_question=1&comment_c=1&comment_answer=1&page_p=1&within=1+day&date=
Many of them point you here: http://docs.vanillaforums.com/developers/troubleshooting/
You need to tell us what the error is before we can help
there's even a picture for you.
I may not provide the completed solution you might desire, but I do try to provide honest suggestions to help you solve your issue.