More information needed...
"I couldn't see any menu links to use".
Do you mean that the entire top menu bar in the admin area disappeared? Please provide a screenshot to clarify.
When i tried to access the admin login page as well as the index page I couldn't.
What exactly happened? Do you get an error message? A blank page? More information please..
Also, seeing that the other two sites are updated properly, the third site is probably different. Maybe it it useful to examine the differences, such as different themes, plugins, and so on.