Can't log in to Admin CP... tool.php produces blank page
 

This is a 3.7 forum that is going to be upgraded. I cloned the database to make a test board. The test db has a different name than the live board, and I set a different cookie prefix in config.php.

First problem:
Logging into the test board Admin CP just loops me back to the login screen.

Second problem:
I uploaded tools.php to try some things with that, but all I get now is a blank white page.

Suggestions on how to fix?