I also verified that when I updated my WordPress environment yesterday (4-08-2104), if I don’t disable the active plugins, I can not access the Administration area of WordPress. I also try to change the theme, and the problem persists. I Only can work if I disable the plugins.
I also verified this problem happens with others developers, look:
1ºhttps://wordpress.org/support/topic/dashboard-wont-show-after-login?replies=3#post-5862681
2ºhttps://wordpress.org/support/topic/pages-not-visible-3?replies=3#post-5862708
