BuddyPress.org

Okay, to recap:

• You are running a new install of WPMU 2.7.1 with BuddyPress 1.0
• You’ve activated BuddyPress
• You have no other plugins installed and activated
• You are using the bphome and bpmember theme
• You do not have any errors AT ALL in your server’s log files
• You’ve installed WPMU as a subdirectory install
• But, you are not positive if WPMU was working before you installed and activated BP

Now, if I understand your issue correctly, when you visit your domain, you can see the home page without any issue. It works fine. But when you click on any link it brings up a blank page without a 404 message.

Or, is it that everything works fine. You can see the home theme and get to the member theme without any problem. You are only seeing this issue when you provide a bogus url. It is only then that you get the blank screen? So, you are wondering why it is not a 404 page.