Do you want to see the error? I also wanted to, but it turned out to be difficult, I did enable showing errors in global joomla.
I did it in the php.ini file fillet I have done in hosting panel. Mistakes I did not see. Just a white screen, I can give you access to the admin panel. What status do you need? administrator or Super User ?
White screen does not happen without a reason. There has to be some kind of a Fatal Error to do that. If Your errors cannot be forced to be displayed than maybe they are being stored in some log file. I think best would be to ask Your hosting provider what to do to know what this error is. An access to joomla panel will not help me in this case.
Before update 05-Feb-2016 15:00:14 Europe/Moscow] PHP Warning: require_once(1/platform.php): failed to open stream: No such file or directory in /home/k6906/6906.ru/docs/libraries/import.legacy.php on line 42 [05-Feb-2016 15:00:14 Europe/Moscow] PHP Fatal error: require_once(): Failed opening required '1/platform.php' (include_path='.:/home/k6906/6906.ru/php') in /home/k6906/6906.ru/docs/libraries/import.legacy.php on line 42 after update
Ok, now it's clear that problem is with JPATH_PLATFORM variable. Somehow the value of it is "1" instead of the path to platform folder. But I'm afraid I will not be able to help with this. You need to talk to joomla support. I've found a report of this exact issue, but there is no answer to that yet: http://forum.joomla.org/viewtopic.php?f=706&t=894659