[DS]

Have a log in option in the sidebar of all pages of your website ..Make sure it is shown only to a user who has not logged in…For this you should create a new sidebar.php and just copy the code from the BP sidebar.php…Hope u got it…

[DS]

Try deactivating the recently added or recently updated plugins…It may solve your problem…I had the same problem too…After deactivating a plugin named site creation wizard my site returned to normal state…
If the problem remains,tell me which theme you use and give me your site url…