Janet,
When I try to login, I see a blank white page. That's usually an indication of a PHP error on the page. Can you set Error Reporting to "maximum" in the Global configuration area of Joomla? Then, either try to login, or let me know, and I can login (if you don't see a similar problem). A more useful error message will hopefully appear.
Either way, another thing to look at that can be a common problem, is to disable any JFBC Profile plugins that you may have enabled that aren't necessary. For instance, if you have the JFBC Profile - JomSocial plugin enabled, but don't have JomSocial installed, disable that plugin. Do that for any profile plugins you may have enabled, and that may clear up your issue as well.
Let us know how that goes,
Alex