ahh the double UserCP menu has been reported before, I have tested in all possible environments and cannot duplicate. Might need FTP access to troubleshoot this further.
Blank page would indicate a suppressed error, try enabling debugging (still done in index.php) and you should see a MySQL error. It sounds like a plugin is uploaded but not installed, you could also try clicking the install icon beside each plugin in the plugin manager to ensure they are all installed.