Hey Samuel,
Do you get this blank page everywhere or just in the backend of CMandrill.
Blank page indicates a fatal error that is not shown on the page, due to your system settings. Go to global config -> server -> set error reporting to developer. Then navigate again to the cmandrill page and let me know what the error is.

If you get a fatal error everywhere, then it still means the same, but you'll have to first deactivate the plugin through the database in order for the page to load normally.
But first let me know what exactly is going on and I'll help you further.

Regards,
Daniel