I have done a quick rebuild, repaired relationships and roles but the issue persists. I have been having issues in the past wrt permissions, but for the most part, everything seems to be working.
I am using Version 7.11.8, Sugar Version 6.5.25 (Build 344), installed locally on a Mac.
Blank screens normally leave a FATAL error in your web server log (the one defined in your php.ini)
Also, are you actually running this on localhost? Or did you just forget to set (during installation) the values that go into config.php, called site_url and host_name?
In Admin / Diagnostics / phpinfo you can see your php.ini path. It’s important that you know this. while you’re looking at phpinfo, you can check your error log location also.