I have the same problem when i go to my blog (www.qwmagazine.co.uk). I have logging in on different browsers and the result is the same – a blank page. I cant access ANY of my pages to deactivate a plugin.
PLEASE keep in mind I have little knowledge of coding etc. so make the advice simple.
Note: this issue started after I installed a new theme. How can I go back to the old theme with no access to my dashboard?