Site administration---Development---Debugging in that Debug Messages Set to extra moodle debug messages for developers
and then check the error exactly what happen..................
line 1478 of \lib\dml\moodle_database.php: call to moodle_database->get_record_select()line 559 of \lib\datalib.php: call to moodle_database->get_record()line 742 of \lib\setup.php: call to get_site()line 26 of \config.php: call to require_once()line 3 of \admin\settings.php: call to require_once()