Admin Panel problems

For some reason when I go into the admin panel to look activate a new account, I update the profile, click on save, and then it reverts back to the home page of the admin panel without saving...........this problem only started tonight.

The page 3 does not exist

what do you mean page 3 does not exist, I havnt mentioned page 3?

When I click save to activate a new member, rather than saying the profile has been updated, it keeps reverting back to the home page of the administration panel, and any amendments ie: accounts activated, have not been actioned?