Reading through this post. I'm wondering this is what I'm experiencing. My forum seems to work until I try to access Control Panel, which gives me a blank screen. Out of desperation and frustration, I've tried starting fresh on a newly formatted linux machine with a new install of the software (not using my old data to rule out corruption). To replicate the error, I'm using a freshly formatted ubuntu LTS LAMP server and am following the install instructions step by step. Everytime, I end up with a working forum with a broken control panel.
I don't believe the issues are the same, but in any case I believe your issue is a bug in the dashboard page itself which is why he can't access that page; you should be able to access other Control Panel pages, try landing on any other admin page such as:
/admin/phpinfo.php
/admin/primary.php
As for the blank dashboard, please see the proposed fix
here.
