We've received a couple of other reports of the web pages freezing and after further investigation it appears to be an unusual intermittent bug where a dashboard tool-tip/help text fails to load correctly.
We're working on a fix for this, but in the meantime the good news is there is a very quick workaround that should allow all the site functionality to become re-enabled.
Please try logging in and when you are on the frozen page tap the right arrow on your keyboard several times. You should then find that the menu buttons and site functionality becomes active again.
Please let us know if the site remains frozen after trying this, and which browsers (including version) this is occurring on.